The Nature Corner

Starting An Aquarium: 7 Easy Steps

March 31, 2026
Having your very own fish tank is a source of endless entertainment and relaxation, but starting an aquarium can be overwhelming!

Unfortunately, it’s not as simple as plopping a fish into a bowl of water. Setting up a successful aquarium requires careful planning and lots of patience. You have to pick compatible species, get supplies like a water conditioner and a heater, cycle your tank, and slowly acclimate your fish.

Starting an aquarium is a daunting task, but the fact that you are here means you have a great start on one of the most important, yet often overlooked, aspects of fishkeeping: doing research! I’ve even made a super-cute shopping list so that you can be fully prepared when you begin setting up your tank.
Shopping List

Here is a basic list of supplies you need for starting an aquarium!

7 Steps for Starting an Aquarium

Step 1: Choose An Aquarium Size

When starting an aquarium, which comes first: the fish or the tank? Before you ever even choose your fish, you should decide what size aquarium is best for you. Some people choose the fish first, but there is nothing worse than falling in love with a species, only to realize that you can’t house it!

Choosing a fish tank comes down to a couple of things: how much space you have and how much maintenance you are willing to do.

Space and Weight Constraints

Aquariums, no matter the size, take up space. If they didn’t, I would be unstoppable. The standard 5-gallon aquarium (~20 L) has a footprint of 16 x 8 inches (~41 x 20 cm), and a height of 10 inches (~25 cm). Before starting an aquarium, think about where you want to put it and what you are going to put it on—this is important, because aquariums are heavy.

A gallon (3.7 L) of water weighs just over 8 pounds (almost 4 kg), and that’s not including the weight of gravel, decor, and the aquarium itself. Your little 5-gallon fish tank could weigh as much as 50-70 pounds (23-32 kg)! So, the dresser or nightstand in your bedroom might seem like the perfect place for a relaxing fish-viewing experience, but it may not be able to support anything too large. When in doubt, purchase an aquarium stand that is designed to hold a heavy tank.

When you venture into keeping larger aquariums (like 125 gallons / 473 L), you have to consider if your floor can support 1500 pounds (~680 kg).

Maintenance Requirements

Aquariums are relaxing, rewarding, and fun! But they take work. Setting up a low-maintenance ecosystem is possible, but it takes a while to get the hang of things. I recommend that beginners stick to a weekly or biweekly water change schedule of about 25% each time. This is manageable on tanks 20-gallons and smaller, but it becomes more of a workout as you go up in size (unless you have an automatic water changer like a Python or a Hygger).

Because of this, many new fish owners believe that smaller tanks = less maintenance, but this could not be further from the truth. Choosing a tank that is too small is one of the most common beginner aquarium mistakes.

The smaller the aquarium, the faster it is going to get dirty and the more susceptible it will be to potentially disastrous parameter swings. So, while a 2.5-gallon (~10 L) tank might seem like the perfect size for your kid’s first tank (water changes will be less than a gallon), you are going to have to do changes more frequently than you would on a 5- or 10-gallon.

In addition, small tanks are more susceptible to things like temperature or pH swings, which can shock your fish. A larger volume sort of acts like a buffer, keeping any changes gradual.

Step 2: Research Possible Species

Once you’ve settled on a tank size, it’s time to pick out your fish! Don’t buy them yet. This is the planning stage, which is arguably the most fun part of starting an aquarium.

While it is tempting to run along the fish wall of your local pet store and get a fish in every size, shape, and color, you must restrain yourself. Not all fish will live together. Some need to be in groups, and some need huge tanks. Some like warm water, others like cold. Other fish, like the popular neon tetra, should placed in aquariums that have already been established for months due to their need for stability. Your first fish should be hardy and suitable for your tank size.

Either the internet or the fish store can advise you on the minimum tank size for the species you are interested in.

Bettas are a hardy, beginner-friendly species. However, they are very aggressive and should not be kept with others of their kind.

If you have met that minimum, the general rule for most species is one inch of adult fish per gallon of water. It’s not perfect, but it will get you in the ballpark of an appropriately stocked tank.

I recommend looking at stocking calculators like AqAdvisor for a better picture of how your stocking works with your tank size and filtration!

Step 3: Gather Supplies

Time for the second-most fun (and most expensive) part of starting an aquarium: getting all of the supplies you need to set it up and keep it going!

Substrate

Substrate is the stuff you put on the bottom of your tank, typically sand or gravel. Some people choose to have bare-bottom tanks (no substrate) because they are easier to clean, but having substrate allows fish to exhibit more natural behaviors—plus, it just looks nicer!

Pet stores sell substrate in all kinds of colors, so it really comes down to your personal preference. I have found that fish look better on darker or more natural-looking colors, like tan, brown, or black.

What substrate is best?

Both sand and gravel are perfectly fine substrates! However, sand shows debris more than gravel, but it can be also easier to clean since everything just sits on top.

When choosing your substrate, you should take your future fish into account. Sand is the preferred substrate for goldfish, cichlids, and bottom-dwelling species like cories and loaches, because they like to sift through it when they look for food, and it’s gentle on their delicate barbles.

How much substrate do I need?

A good rule of thumb is one pound of substrate per gallon of water. You may need more or less if your tank has a unique footprint. If you are planning to have live plants, it is best to get enough sand or gravel to make your substrate 2-3 inches (~5-8 cm) deep.

Decor

Picking out decor is another really fun part of starting an aquarium. This is where you get to let your creativity shine! Whatever you choose, make sure it is aquarium-safe and won’t alter your water chemistry (seashells will alter your parameters).

Sunken shipwrecks, princess castles, and volcanoes, oh my! Pick out some fun and funky decor, or go the natural route with some river rock, dragon stone, and driftwood. Pick out some fake plants or flex your aquatic green thumb and grow some real ones.

Live plants make beautiful decorations for aquariums, and they help a little bit with water quality.

It’s really hard to overcrowd your tank with decor. As long as your fish still have room to swim, they’ll probably appreciate all of the hiding places! Some fish, like plecos and peacock gudgeons, love caves. Just make sure that there aren’t any tiny holes that your little friends could get stuck in.

Water Conditioner

Water conditioner, also known as dechlorinator, is the most important chemical to add when starting an aquarium. In fact, you should use it any time you are adding water to your tank, even if you are just doing a water change or replacing evaporated water.

Many municipal water supplies contain small amounts of chlorine and/or chloramine. Chlorine will evaporate out after several hours, but chloramine and heavy metals do not. Water conditioner works by breaking chemical bonds, breaking up dangerous compounds into their ion components, which are harmless. Check out this video below that explains a bit more about how dechlorinators work:

Heater (if needed)

Heaters are often overlooked supplies when new fishkeepers are starting an aquarium. Many beginner-friendly fish, like platies and tetras, like their water in the mid-to-upper 70s (F). Even if a fish doesn’t need warm water, having a heater in the tank can help keep the water temperature stable.

Aquarium heaters come in many different wattages, and it can be overwhelming trying to choose the one best for your tank size!

Heaters are best placed by the filter, so that the pump can help circulate the warm water throughout the tank, creating a stable environment for your fish and also helping ensure the temperature regulation of your heater functions properly.

Filter

Filters are a critical part of a successful aquarium. In addition to removing large particles from the water, they provide water movement, oxygenation, and a place for beneficial bacteria to grow. There are several different kinds of filters, but we’ll just touch on a few of the most common ones.

Hang-on-back

Hang-on-back filters are the most common filter choice for starting an aquarium. They get their name because they hang on the back of your tank. They can be external or internal. Maintenance for a hang-on-back filter is pretty straightforward: rinse out the media whenever it gets clogged, and rinse out the filter compartment with old tank water once a month or so. If you are using carbon cartridges, they must be replaced every 1-2 months (which isn’t great for the long-term stability of your tank, so I do not recommend using cartridges. It’s low-key a scam by Big Aquarium.)

Sponge

Sponge filters are probably the second-most popular form of filtration. They are especially desired for shrimp, bettas, or baby fish (fry), because they are super gentle, and their dense foam prevent even the smallest of fish from getting sucked up.

Sponge filters are slightly more complicated than hang-on-back filters because you need the sponge itself, airline tubing, a check valve, and an air pump. They still need to be rinsed out every now and then because they eventually get clogged.

Canister

Canister filters are one of the more advanced and expensive types of filters, but they do a great job of dealing with large, high-bioload tanks. They also require the least amount of maintenance and can go anywhere from 2-6 months (or even longer!) without being cleaned.

Step 4: Cycle Your Tank

Now it’s time for the hardest part of starting an aquarium, the phase most often overlooked and that can lead to your fish dying “for no reason”: cycling.

“Cycling a tank” refers to the process of establishing the nitrogen cycle in an aquarium. Failing to do so often results in fish death.

What is the nitrogen cycle?

The nitrogen cycle is the process of toxic compounds from fish waste being converted into less-toxic forms. Through things like poop, fish urine (yes, they pee), and uneaten food break down into ammonia. Ammonia is toxic in any amount to your fish, so you want it to be 0 at all times.

A group of beneficial bacteria (Nitrosomonas) converts the ammonia to nitrite, which is also pretty toxic and should be at 0.

A second group of good bacteria (Nitrobacter) converts nitrite into nitrate, which is only toxic when it reaches levels above 40 ppm. You want your nitrate to be as low as possible, but it’s okay if you have a little bit.

When a tank is “cycled,” ammonia is almost immediately converted into nitrate, which is then removed by water changes and/or live plants. Ideally, you want to establish your tank cycle before adding fish, so that your new babies don’t have to experience the damaging effects of ammonia.

Fishless cycles

Fishless cycles are the best cycles. They are completed before adding fish. They involve dosing the tank with pure ammonia (I like Dr. Tim’s!) or something that produces ammonia, like fish food. Some people keep their empty tanks cycled by throwing in a piece of raw shrimp. When they are ready to add fish, they remove the shrimp, test the water, and do a water change.

Fishless cycles can take a while, up to two months, but the wait is worth the peace of mind that your fish will have a nice, stable environment. You can speed up the process by adding bottled bacteria, like Seachem Stability, FritzZyme TurboStart, or Tetra Safe Start.

Fish-in cycles

Fish-in cycles are the least recommended form of cycling, but they are the most common. In this kind of cycle, you add your fish and pray. If attempting a fish-in cycle, only add a few fish at a time. Do not stock your tank more than 25%. You also have to be mindful of the ammonia levels in your tank, keep an eye on your fish’s behavior (like gasping at the surface) and potential symptoms of trouble (like ammonia burns). Fish-in cycles require more frequent water changes to keep your fish from perishing due to toxic nitrogen compounds. Fish-in cycles can also benefit from bottled bacteria.

Step 5: Buy Your Fish!

Okay, I lied. Buying your fish is the most fun part of starting an aquarium! By the time you’ve gotten to this point, you should have done enough research to know how many fish and what kinds will do best in your tank. Fish store employees are more than happy to lend a guiding hand, but it’s always good to come prepared.

Picking out healthy fish

Give your aquarium the best possible start by selecting fish that aren’t showing signs of disease. Obviously, you don’t want to bring in sick fish! The process of leaving the store and acclimating to a new aquarium is very stressful, and fish that are unwell will have a harder time coping with change.

Healthy fish are active and vibrant. They have good body condition and don’t have any white or red blotches (outside of normal coloration for the species). It is important to familiarize yourself with some of the common diseases that affect freshwater aquarium fish so that you know what to look for!

When starting an aquarium, choose fish that are active, robust, and vibrant.

When picking out your fish, avoid individuals that:
- Have torn or missing fins
- Have cottony growths anywhere on their body
- Look like they are covered in salt
- Have red blotches, wounds, or ulcers
- Are abnormally skinny or have a sunken belly
- Have white, stringy poop
- Are shimmying in place
- Are staying at the top or bottom of the tank
If a store has a large number of diseased or dead fish, get your fish from somewhere else.

Step 6: Acclimate Your Fish

One of the most important steps of starting an aquarium is acclimating your fish properly. “Acclimating” refers to getting your fish used to your tank’s water before setting them free. Good acclimation lets fish gradually adjust to both temperature and water chemistry.

Temperature acclimation

Temperature acclimation is the bare minimum when it comes to acclimation. Before releasing your fish into your aquarium, you should float them in a container (usually the bag you brought them home in) for at least 15-20 minutes. This allows the fish to get used to the temperature of your tank.

If you don’t perform this crucial step, there is a chance that the temperature change could stress them so badly that they get sick—or even die.

Other parameters

If your tank water is very similar to the water the fish are currently in, you might skip this step. Plenty of people do, and their fish end up fine. However, I recommend doing a slightly more extensive acclimation process to make sure your fish are used to things like pH, water hardness, and other parameters—not just temperature. There are a couple of different ways to achieve this:
- Option 1: Float, then add tank water
  - After your fish have completed their temperature acclimation, add a little bit of tank water to the bag.
  - Wait 10-15 minutes.
  - Add a little bit more tank water.
  - Repeat 2-3 times.
  - Release the fish into the tank (net them out or something; avoid getting store water in your tank)
- Option 2: Drip acclimation (floating is the last step)
  - Put fish into a stable container—you can leave them in the bag (make sure it won’t fall over), or dump them into a fish-safe bucket or tub. I like to use a little critter keeper.
  - Using a bit of airline tubing, get suction going to drain water from your tank—do not drain it directly into your fish receptacle yet.
  - Tie a knot in the tubing to reduce the water flow so that it is just dripping out—about 2-4 drops per second. You may go even slower if you are acclimating a sensitive species.
  - Wait for the water volume to double or triple. This usually takes 30 minutes to an hour.
  - Put the fish (with some of their new, mixed water) back in the bag, or something else small enough to float in your tank.
  - Temperature acclimate!
  - Release the hostages (again, avoid getting the store water in your tank.)
Here is a neat video explaining drip acclimation:

Step 7: Let Your New Fish Get Settled In

After starting an aquarium, it is tempting to leave your tank lights on to watch your fish explore. However, I recommend leaving the lights off for at least 4 hours. The dark helps keep the fish calm, making the transition as stress-free as possible. Some people leave the lights off for the rest of the day.

When the tank lights come on, you can try offering a tiny bit of food to help them feel comfortable, but don’t worry if they don’t eat anything right away. Some people don’t feed their new fish for at least 24 hours after bringing them home, since they are likely to refuse it, resulting in uneaten food rotting in the tank.

Conclusion

Starting an aquarium can be overwhelming, especially for beginners. But by reading guides like this one, you are helping to set yourself—and your new fishies—up for success!

Many issues encountered by new aquarists can be easily avoided if you do your research and have patience. By planning carefully, using dechlorinator, cycling your tank, and gently acclimating your new fish to your aquarium, you greatly reduce the chance of their untimely demise.

Congratulations on your new aquarium! Now it’s time to keep your fish happy with regular tank maintenance.

Thanks for reading, and happy fishkeeping!
15 Of The Best Algae Eaters By Tank Size

March 9, 2026
How do you get rid of algae in a fish tank? While there are many ways to control algae, many aquarists opt for the easiest and most fun solution: add an algae eater!

But not all algae eaters are created equally. Some get way too big for most aquariums, are aggressive, or don’t actually eat algae at all. Regardless of the fish or invertebrate you choose, you should remember that your algae eater is another living creature that you must care for; it must be fed (more than algae) and cleaned up after.

What is the best algae eater?

It depends on many factors: how big your tank is, what kind of algae you are dealing with, and other details of your setup.

Before we talk about what the best algae eater is based on your tank size, we’ll talk about why they aren’t required for a healthy aquarium.
Do You Have to Have an Algae Eater?

While “suckerfish” are often touted as necessary inhabitants for your tank, they are completely optional! Algae is a little ugly, but won’t hurt your fish. Algae eaters can be fun and interesting additions to your aquarium, and they can help you manage that delightful green slime coating every surface of your tank. However, it is important to note that algae eaters simply turn algae into poop, and the increased bioload in your tank may actually mean more maintenance.

Algae eaters are your little helpers, not tiny janitors responsible for keeping the tank clean. If you are prepared to feed, house, and tend to another fish in your tank, now it’s time to decide what algae eater is best for you, based on your tank size.

Best Algae Eaters for 5+ Gallon Tanks

Nerite Snail (Neritina sp.)

Nerite snails are great algae eaters for small tanks because they come in tons of fun colors (spots, strips, and more!), don’t get huge, and don’t reproduce in freshwater! They are easy to care for, and they will make quick work of an algae problem. I had a little horned nerite in my college betta tank, and I never had to clean off any algae myself, despite the lights being left on all. day. long. A female nerite snail may lay little white eggs all over the aquarium, but they will not hatch successfully. Eggs can be removed with an algae scraper or a strong fingernail.
- Adult size: up to 1 inch (2.5 cm), species dependent
- Minimum tank size: 5 gallons (~20L)
- Supplemental foods: picky; can offer algae wafers and blanched vegetables
- Care difficulty: easy
- Species notes: won’t reproduce in freshwater; eggs can be scraped off
My college roommate, a horned nerite snail that kept the tank pristine

Amano Shrimp (Caridina multidentata)

Amano shrimp are the best algae-eating shrimp, and one of the best algae eaters overall. They are positively voracious when it comes to green slime! While they are much more difficult to breed than cherry shrimp (requiring brackish water to reproduce), they will make short work of your algae problem, whether you are dealing with brown diatoms, hair algae, black beard algae, or green spot algae.
- Adult size: 2 inches (5 cm)
- Minimum tank size: 5 gallons (~20 L)
- Supplemental foods: algae wafers, shrimp pellets, blanched vegetables
- Care difficulty: moderate
- Species notes: require a stable and established aquarium; keepers must monitor mineral levels
Cherry Shrimp (Neocaridina davidi)

Despite their name, cherry shrimp come in a huge variety of colors other than red. I personally have a colony of little orange ones! Cherry shrimp love to chow down on algae and biofilm, but they are too small to make an appreciable difference in an algae-infested tank. They are best at keeping algae from getting out of hand in an established aquarium.
- Adult size: 1.5 inches (4 cm); females larger than males
- Minimum tank size: 5 gallons (~20 L)
- Supplemental foods: algae wafers, shrimp pellets, blanched vegetables
- Care difficulty: moderate
- Species notes: require a stable and established aquarium; keepers must monitor mineral levels
My Sunkist orange “cherry shrimp” dining on some bottom feeder pellets with a few ramshorn snails

Ramshorn Snail (Planorbella sp.)

Often considered to be “pest snails,” ramshorns are exceptional algae eaters and are found in a variety of colors, from blue to pink, solid to spotted. I recommend at least a 10-gallon tank for ramshorns for one reason: while these snails stay small, they will reproduce rapidly in environments with adequate food. The snails are hermaphroditic (having both male and female reproductive organs) and can store reproductive material (snail sperm…snerm) for a long time, possibly even over a year. A hitchhiker or two on a new plant could lead to your tank being overrun by tiny mollusks.
- Adult size: 1 inch (2.5 cm)
- Minimum tank size: 5 gallons (~20 L) if you carefully manage population
- Supplemental foods: algae wafers, blanched vegetables, snello, cuttle bone for calcium, sinking pellets
- Care difficulty: easy
- Species notes: can overpopulate a tank if food is not limited
Best Algae Eaters for 10+ Gallon Tanks

Otocinclus (Otocinclus sp.)

Otocinclus (or simply known as otos or dwarf suckermouth catfish) are small schooling catfish that are very effective algae eaters. Their favorite kinds of algae are the softer varieties like brown diatoms or some forms of green algae. They are schooling fish and should be kept in groups of at least six individuals. Despite their small size, their social requirements and sensitivity to sudden changes in water parameters make them need a larger tank than you’d expect.
- Adult size: 2 inches (5 cm)
- Minimum tank size: 10 gallons (~40 L)
- Supplemental foods: algae wafers, blanched vegetables, BacterAE, Repashy Soilent Green
- Care difficulty: moderate
- Species notes: many otos are wild-caught and can be picky with their food and water
Mystery Snail (Pomacea diffusa)

Mystery snails get a little bit larger than their nerite cousins, and they eat a wider variety of foods. They will happily munch on algae and biofilm, but they will also eat leftover fish food, sinking pellets, and dying aquarium plants (but they usually don’t touch healthy ones). These snails are pretty hardy, but keep an eye on their shell health! If the pH is too low or if there isn’t enough calcium in their water or diet, their white, gold, purple, black, or blue shells may become noticeably brittle.
- Adult size: 3 inches (7.6 cm)
- Minimum tank size: 10 gallons (40 L)
- Supplemental foods: algae wafers, blanched vegetables, snello, cuttle bone for calcium, sinking pellets
- Care difficulty: easy-to-moderate
- Species notes: monitor pH and water hardness; provide supplemental calcium for shell health
One of my magenta mystery snails searching for algae and biofilm on the tank wall

Best Algae Eaters for 20+ Gallon Tanks

Bristlenose Plecostomus (Ancistrus cirrhosus)

One of the most popular algae eaters for medium-sized tanks is the bristlenose pleco. This dwarf pleco species gets its name from the branch-like protrusions that mature males develop on their snouts. They are hardy, forgiving of many beginner mistakes, and get along with a wide variety of tankmates, although males can be territorial towards each other. In addition, they are one of the easiest pleco species to breed and have been cultivated in several fun varieties, like albino, lemon blue-eye, red, green dragon, and marbled.
- Adult size: 5 inches (12.7 cm)
- Minimum tank size: 20 gallons (~80 L)
- Supplemental foods: algae wafers, sinking pellets, blanched vegetables,
- Care difficulty: easy
- Species notes: males are territorial with each other
A bristlenose plecosomus cleans algae off of aquarium glass. Photo by Cristobal Sabajtis on Unsplash

American Flagfish (Jordanella floridae)

The American flagfish (or Florida flagfish, or just flagfish), is one of the few creatures that will eat the most cursed of algae: hair and black beard. These fish, native to the state of Florida, thrive in unheated tanks. They can be kept at temperatures from 64-80° F (18-27° C), with the optimum temperature range being 68-72° F (20-22° C). They can be kept with a wide variety of peaceful tank mates, but they may eat shrimp.
- Adult size: 2.5 inches (6 cm)
- Minimum tank size: 20 gallons (~80 L) for a pair
- Supplemental foods: most commercial fish foods, as well as algae wafers; not picky
- Care difficulty: easy
- Species notes: increase tank size if keeping more than one male
Rubber-lip Plecostomus (Chaestoma milesi)

Plecos are one of the most commonly sold algae eaters, but many of the common species get way too large for most aquarists. But not all species grow into 2-foot giants! The rubber-lip pleco is a fun-sized species that stays under 6 inches (15 cm) and still does a great job at helping to keep algae. Also known as the bulldog pleco, this hardy suckerfish gets its name from its blunt, rounded nose. It is brownish-green in color with adorable black spots, and it loves caves and other hiding places.
- Adult size: 5 inches (12.7 cm)
- Minimum tank size: 20 gallons (~80 L)
- Supplemental foods: algae wafers, sinking pellets, blanched vegetables
- Care difficulty: easy
- Species notes: peaceful, but can be territorial toward other bottom dwellers.
Panda Garra (Garra flavatra)

The panda garra is an excellent algae eater that will tackle many kinds of soft algae, including green spot and brown diatoms. They get their name from the alternating bands of brown and yellow down their bodies. While they can be kept in community setups, they can be aggressive upon reaching maturity, especially the males, and they may not make good tank mates for every fish. As with any new fish, make sure to research species compatibility and get anecdotes from other fish keepers about their experiences.
- Adult size: 3 inches (7.6 cm)
- Minimum tank size: 20 gallons (~80 L)
- Supplemental foods: algae wafers, sinking pellets, blanched vegetables, frozen bloodworms and brine shrimp
- Care difficulty: moderate
- Species notes: social—keep in groups of 5+; like tanks with high oxygen
Hillstream Loach (Sewellia lineolata)

Hillstream loaches are great algae eaters for coldwater aquariums. Their wing-like pectoral and pelvic fins have earned them the additional nickname of “butterfly loach.” Hailing from the streams of southeastern Asia, these funky little guys need high-flow aquariums to mimic their natural habitat. They also prefer to be kept in groups of at least three individuals, with larger groups allowing their keepers to witness more natural behaviors.
- Adult size: 3 inches (7.6 cm)
- Minimum tank size: 20 gallons (~ 80 L)
- Supplemental Foods: algae wafers, blanched vegetables
- Care difficulty: moderate
- Species notes: need high-flow tanks; keep in groups of 3+ individuals
Hillstream loaches are weird little fish that are great at eating algae in high-flow tanks. Photo by ק. פ. on Unsplash

Best Algae Eaters for 55+ Gallon Tanks

Siamese Algae Eater (Crossocheilus oblongus)

Unlike most of the other species on this list, the Siamese algae eater (SAE) will eat almost any type of algae, from soft brown diatoms to the infamous hair algae. SAEs are relatively peaceful with other fish, but they are voracious eaters and should be paired only with speedy species that can compete with them for food. They can also be territorial with one another, so keep at least three individuals together if keeping multiples to disperse aggression. They can be kept as a single specimen, but some keepers note that they can be shy when all by themselves.
- Adult size: 6 inches (15 cm)
- Minimum tank size: 55 gallons (208 L)
- Supplemental foods: sinking pellets, algae wafers, blanched vegetables
- Care difficulty: moderate; can be temperamental
- Species notes: can be territorial; keep singly or in groups of 3+
Siamese algae eaters are one of the few species that will eat hair algae

Green Phantom Plecostomus

The green phantom pleco looks like a species from another planet with its unique, green-gold coloration. While not as enthusiastic as the Siamese algae eater, green phantoms will reduce some of the soft, easily consumed algae in your tank. If you are looking for an interesting, mid-sized pleco that will also help out a little with tank maintenance, a green phantom may be right for you! While they are an “algae eater,” they are omnivorous, and they still need to be supplemented with other foods.
- Adult size: 7 inches (18 cm)
- Minimum tank size: 55 gallons (208 L)
- Supplemental foods: algae wafers, blanched vegetables, frozen bloodworms and shrimp
- Care difficulty: moderate
- Species notes: sensitive to poor water quality and needs varied diet
Best Algae Eaters for Very Large Aquariums (125+ Gallons)

Common Plecostomus (Hypostomus plecostomus)

I am a firm believer that common plecos, one of the most readily available algae eaters, should only be sold in specialty fish stores—if they are sold at all. The cute little suckerfish at your local pet store may only be two or three inches long, but they have the potential to become two-foot monstrosities. When I was a child, my family made the mistake of putting one of these guys in a ten-gallon. This single fish produced piles of poop. While they are effective algae eaters, they need huge tanks to accommodate their giant size and matching bioload.
- Adult size: 24 inches (60 cm)
- Minimum tank size: 125 gallons (~470 L)
- Supplemental foods: algae wafers, blanched vegetables, occasional meaty fish foods
- Care difficulty: moderate
- Species notes: need huge tanks!
The common plecos you see in fish stores are babies. They get very large and are unsuitable for most home aquariums.

Sailfin Plecostomus (Pterygoplichthys gibbiceps)

Similar to the common pleco, the sailfin pleco also gets massive and is one of the best algae eaters for large tanks. It gets its name from its huge dorsal fin that resembles a sail. With proper care, these stunning fish can live to be 20+ years old. While they do eat algae and other plant material, they also require some soft driftwood to help their digestion.
- Adult size: 20 inches (50 cm)
- Minimum tank size: 125 gallons (~470 L)
- Supplemental foods: algae wafers, blanched vegetables, occasional meaty fish foods, driftwood
- Care difficulty: moderate
- Species notes: get huge; require driftwood for digestion
Frequently Asked Questions

Are Chinese algae eaters good algae eaters?

Chinese algae eaters (sometimes labeled simply as “algae eaters”) are decent at eating algae while they are young, but this changes as they age. As the fish matures, it begins to seek protein, which it tries to obtain by eating its tankmates. CAEs are semi-aggressive and should only be kept with other semi-aggressive fish that can hold their own. Also, they can reach 10 inches (25 cm) in length.

Are clown plecos good algae eaters?

The clown plecostomus is not an effective algae eater. While some other plecos are voracious algae eaters, clown plecos prefer to rasp on driftwood. They might nibble on some algae every now and then, but they need soft wood in the tank for their digestion. I had a clown pleco for several years, and there was never an appreciable difference in algae until I took steps to manage the algae myself.

Clown plecos are adorable with their little yellow stripes, but they aren’t great at eating algae.

How can I manage algae without an algae eater?

While the fastest way to get rid of algae is manual removal with an aquarium-safe sponge or scraper, it isn’t a long-term solution. Algae is caused by an imbalance of light, nutrients, and carbon dioxide. Reducing the length of time your aquarium light is on will help. Performing larger or more frequent water changes will cut down on the organic matter available to the algae, and live plants will compete against it for resources. Advanced aquarists may want to experiment with supplementing carbon dioxide, which will give plants the boost they need to win against an algae epidemic.

Conclusion

While it might be ugly, algae isn’t harmful to fish. Nevertheless, an algae eater can help you keep algae in check and also be an interesting member of your underwater community. While algae eaters are helpful, they do not replace tank maintenance and still require supplemental food. Few organisms can survive on algae alone!

Whatever algae-munching critter is right for you, make sure to plan for its adult size. The two-inch pleco in your local pet store won’t stay that small forever. Even if a fish stays small, it may benefit from the stability of a larger aquarium.

As always, make sure you do your research, and happy fishkeeping!
16 Amazing Beginner-Friendly Fish That Are Easy To Take Care Of

January 23, 2026
Aquariums are a relaxing and enjoyable hobby. Watching the fish swim through crystal-clear water, forage for food, and interact with each other is a lot of fun! However, there is a lot that goes into setting up an aquarium correctly. When learning the basics, new fish keepers often find it helpful to stock their aquariums with hardy fish that are easy to take care of.

From bettas and tetras to mollies and the cutest catfish you’ve seen in your life, there are plenty of beautiful species that are forgiving toward beginner mistakes.

Before we dive into this list of fish that are easy to take care of, let’s talk about what it means for a fish to be “beginner-friendly.”

What Makes a Fish 4″Beginner-Friendly”?

I’ve carefully compiled this list using my own experience as a fish keeper and pet store employee, real-world conversations I’ve had with beginner and advanced aquarists, and lots of research. The criteria I’ve used to make this list are as follows:
- Ability to tolerate minor fluctuations in water chemistry (temperature, pH, and nitrogen compounds)
- Minimum tank size requirements
- General health in the pet trade
- Compatibility with tank mates
Some fish touted as “beginner-friendly” do not fit these requirements. For example, fancy guppies were once considered easy, hardy fish. However, the guppies most readily available (those in chain pet stores) are often sickly and inbred, requiring a very stable environment–and sometimes medication–to thrive. I’ve had fish owners do everything “right,” but their guppies still die. For this reason, fancy guppies did not make the list.

Table of Contents
Fish That Are Easy To Take Care Of

There are a lot of fish that are good for beginners. To help you find your way, I’ve divided them into categories: solitary fish, schooling fish, livebearers, and the clean-up crew.

Best Solitary Fish for Beginners

If you want just one fish in your aquarium to let yourself get the hang of things, the following species are great choices. They will fight with others of their kind, and they thrive in solitude.

Bettas (Betta splendens)

Bettas, also known as Siamese fighting fish, are a popular fish for first-time fish owners. They are hardy, colorful, and they don’t need massive tanks or friends. As long as you provide an adequately sized tank and warm, clean water, your betta should do just fine!
- Minimum tank size: 5 gallons (~20L)
- Temperature range: 75-82° F (~24-28° C)
- Max Size: 3 inches (7.62 cm)
- Temperament: aggressive
- Social needs: best kept alone
When given proper care and enough space, bettas’ colors and personalities shine!

Best Schooling Fish for Beginners

The following fish are schooling, which means they like to live in groups! I recommend the following species in groups of 6 or more. If there are too few individuals in a school, they will not feel safe, resulting in your fish hiding and being stressed, making them more likely to get sick. Some schooling fish will also become violent if they don’t have enough friends to harass.

Zebra Danio (Danio rerio)

The zebra danio is one of the most popular aquarium fish for beginners. These zippy little guys are active and hardy. They have a large temperature range, and they are even used in scientific research! They come in short-finned and long-finned varieties, as well as gold and leopard. Some have even been modified with jellyfish DNA (GloFish) and are just as hardy as their unmodified cousins.
- Minimum tank size: 10 gallons (~40 L)
- Temperature range: 65–78°F (~18–25.5°C)
- Max Size: 2 inches (5 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Skirt Tetras (Gymnocorymbus ternetzi)

Skirt tetras are another species that I recommend for your first aquarium. While they do get a little larger than zebra danios and need at least a 20-gallon tank for a school, they are worth it. Their larger size make them easier to see from far away. They come in several varieties, including long- and short-finned, black skirt, white skirt, and Glo-ified. All of the flavors can be mixed together for a beautiful, diverse school!
- Minimum tank size: 20 gallons (~76 L)
- Temperature range: 75-80° F (~24-27° C)
- Max Size: 3 inches (7.62 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Skirt tetras are a beginner-friendly schooling fish that come in multiple colors.

White Cloud Mountain Minnow (Tanichthys albonubes)

If you’re looking for a small fish for a coldwater aquarium, check out the white cloud mountain minnow! They are easy to care for and don’t require a heater in the standard home. Both standard and gold white clouds have a brilliant white stripe down their sides and adorable red fins.
- Minimum tank size: 10 gallons (~40 L)
- Temperature range: 65–75°F (~18–24°C)
- Max Size: 1.5 inches (4 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Rosy Red Minnow/Fathead Minnow (Pimephales promelas)

Frequently sold as feeder fish or as bait, fathead minnows are another hardy fish for a coldwater aquarium. Whether you opt for the silvery wild-types or the pink-toned rosy reds, they can cohabitate with white clouds and zebra danios for a thriving community tank.
- Minimum tank size: 20 gallons (76 L)
- Temperature range: 50-70° F (~10-21° C)
- Max Size: 3.5 inches (9 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Cherry Barb (Puntius titteya)

These peaceful barbs get their name from the vibrant red color sported by mature males. Females are more of an orange-ish brown. While many fish keepers want to have a school made up of cherry-red fish, having a mixed-sex group will encourage brighter colors as the boys try to show off for the ladies.
- Minimum tank size: 20 gallons (80 L)
- Temperature range: 75-80° F (~24-27° C)
- Max Size: 2 inches (5 cm)
- Temperament: peaceful
- Social Needs: schooling (6+); 2F:1M
Check out the video below to learn more about these stunning fish!

Harlequin Rasbora (Trigonostigma heteromorpha)

Harlequin rasboras are another fish that are easy to take care of. These adorable, half-black fish stay small and get along with many other species. Some keepers claim that they are one of the hardiest fish in the aquarium trade, potentially living over 5 years with proper care.
- Minimum tank size: 10 gallons (40 L)
- Temperature range: 72-80°F (~22-27°C)
- Max Size: 2 inches (5 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Glowlight Tetra (Hemigrammus erythrozonus)

The glowlight tetra is a striking fish with a stunning, bright orange stripe running down its silvery sides. If you are looking for some subtle pops of color that rival the electric blue of the more popular neon tetra, a school of glowlights might be just what your are looking for!
- Minimum tank size: 10 gallons (40 L)
- Temperature range: 75-80°F (~24-27°C)
- Max Size: 2 inches (5 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Black Neon Tetra (Hyphessobrycon herbertaxelrodi)

Despite their name, black neon tetras are not super closely related to the standard neon tetra, but they are another beginner-friendly fish that will liven up your aquarium, despite their understated colors. They are also larger, bolder, and hardier than neon tetras, making them suitable tankmates for a variety of species.
- Minimum tank size: 10 gallons (40 L)
- Temperature range: 72–80°F (~22–27°C)
- Max Size: 2 inches (5 cm)
- Temperament: peaceful
- Social Needs: schooling (6+)
Best Livebearers for Beginners

Livebearers get their name because, unlike many other fish, they give birth to live young! While it is super cool to watch, and livebearers are a great introduction to fish breeding, I recommend that new fish keepers only keep one sex–all males or all females. This is because livebearers can quickly overpopulate your tank. When you pick out your fish, ask the fish store employee pick out one sex. It’s important that you also learn how to tell the difference between male and female livebearers so that you can double-check.

If you do decide to keep a mixed group and are prepared for loads of babies, keep 2-3 females for every male. If keeping a same-sex group, aim for at least 3 individuals to disperse any bullying, with 5+ fish being ideal.

Endler’s Livebearer (Poecilia wingei)

The Endler’s livebearer is the fancy guppy’s smaller, hardier cousin. Endlers have a greater tolerance to shifts in water parameters like temperature, and they are less susceptible to disease, making them a great alternative to fancy guppies in the beginner aquarium. While the females are often colorless, the males can display some dazzling hues.
- Minimum tank size: 10 gallons (40 L)
- Temperature range: 65-80°F (~18-27°C)
- Max Size: 1 inch (2.5 cm) for males
- Temperament: peaceful
- Social Needs: groups of 3+
Check out the video below (by the one-and-only Aquarium Co-Op!) for more info about how to care for these awesome little guys:

Platy (Xiphophorus maculatus)

Platies are one of my favorite species of aquarium fish. They come in all sorts of colors, are hardy and peaceful, and are delightfully chunky. If you like the color of goldfish but do not have the space for a 10-inch pooping machine, consider some sunburst or red wag platies for the same vibrance and insatiable hunger in a smaller package.
- Minimum tank size: 10 gallons (40 L)
- Temperature range: 70-82°F (~21-28°C)
- Max Size: 3 inches (7.6 cm)
- Temperament: peaceful
- Social Needs: groups of 3+
Platies are peaceful livebearers that come in a variety of gorgeous colors.

Swordtail (Xiphophorus hellerii)

Swordtails get their name from the long tail extension developed by mature males (and sometimes older females). The “sword” extends from the bottom corner of the tail, often thicker and darker than the rest of the fin. Swordtails are also very closely related to platies, and the two can crossbreed to produce healthy offspring.
- Minimum tank size: 20 gallons (~80 L)
- Temperature range: 70-82°F (~21-28°C)
- Max Size: 6 inches (~15 cm)
- Temperament: peaceful
- Social Needs: groups of 3+
Molly (Poecilia sp.)

Mollies are closely related to guppies and Endler’s livebearers, but they get a bit larger. There are many different species of mollies, from the short and stubby balloon mollies ( to the large, magnificent sailfin mollies. While I recommend at least a 20 gallon for standard mollies, some of the larger varieties like sailfins will benefit from an even bigger tank. With mollies, it is especially important that you have at least three individuals in a group, because they can sometimes be bigger bullies than other livebearers.
- Minimum tank size: 20 gallons (~80 L)
- Temperature range: 72-82°F (~22-28°C)
- Max Size: 4.5 inches (~11.4 cm)
- Temperament: peaceful
- Social Needs: groups of 3+
Mollies are a larger livebearer that can thrive in a variety of conditions. Photo by Vanburn Gonsalves on Unsplash.

Best Bottom Feeders and Algae Eaters for Beginners

The following are beginner-friendly species that will help keep the tank clean. However, owning these species will not replace tank maintenance. They can help you control algae and uneaten food, but you will still have to perform water changes, vacuum your gravel, and take steps to keep algae in check. Most importantly, you still need to feed your clean-up crew. While they will munch on leftover food and algae, you should supplement with sinking pellets and algae wafers to make sure they are getting enough.

It is important to note that no fish eats poop, and your “cleaner” fish will poop, too.

With that being said, the following species are still great additions to your aquarium and can be very fun to watch!

Corydora Catfish (Corydoras sp.)

Many fish keepers refuse to keep a tank without some sort of Corydora catfish snuffling about on the bottom of the aquarium. These silly and peaceful little guys are a schooling species and should be kept in groups of at least six. They will eat any food that falls to the bottom of the tank, but they do not eat poop. You should supplement your cories with some sinking bottom feeder pellets to make sure they get enough food!
- Minimum tank size: 10 gallons (~40L) for dwarf; 20 gallons (~80 L) for standard
- Temperature range: generally 70-80°F (~21-27°C); species dependent
- Max Size: 3 inches (7.6 cm); species dependent
- Temperament: peaceful
- Social Needs: schooling (6+)
Corydora catfish are peaceful, hardy bottom dwellers that do best when kept in groups.

Bristlenose Plecostomus (Ancistrus cirrhosus)

There are many methods for controlling algae in a fish tank, but many fish keepers opt to get an algae-eating fish, too. Many people gravitate toward the common plecostomus, not realizing that they can get to be two feet long! The bristlenose pleco is a smaller and better alternative for most tanks. They get their name from the bushy growths that appear on the noses of mature males. While they leave other fish alone, males can be territorial with one another. I recommend 20 gallons per fish to give each fish its own space, but also to keep your tank from being overwhelmed by pleco poop!
- Minimum tank size: 20 gallons (~40 L) per fish
- Temperature range: 72-82°F (~22-28°C)
- Max Size: 6 inches (~15 cm)
- Temperament: peaceful; males can be territorial toward each other
- Social Needs: solitary or in male/female pairs
Nerite Snail (various species)

Never underestimate the power of a snail. Nerite snails come in various sizes and colors, get along with just about any fish, and do a fantastic job at eating algae! When I was in college, I kept a betta tank on my desk. I left the lights on for at least 16 hours per day (I didn’t get much sleep), but the tiny horned nerite snail in the tank made sure I never had to clean any algae myself. The best thing about nerite snails is that they don’t reproduce in freshwater! That’s right! You can experience the unbridled joy of being a snail parent without worrying about its offspring overrunning your aquarium.
- Minimum tank size: 5 gallons (~20 L)
- Temperature range: 70-80°F (~21-27°C)
- Max Size: around 1.5 inches (~4 cm); species dependent
- Temperament: peaceful
- Social Needs: literally does not care
Nerite snails come in a lot of cool colors and patterns, and they do not reproduce in freshwater!

Frequently Asked Questions

Wondering why a species wasn’t included? Check out our frequently asked questions below!

Are goldfish good for beginners?

While goldfish are very hardy and are forgiving toward many beginner mistakes, they need far more space than people realize, with some experts suggesting 20-40 gallons per fish, depending on the breed. Your little fair goldfish can grow to over 8 inches long, and keeping them in a small tank will shorten their lifespan (which is 10-20 years, by the way). Goldfish are also very messy and need very good filters. Their large size and tendency to be absolutely disgusting make them a poor choice for your beginner aquarium (unless it’s, like, 40 gallons).

Are shrimp good for beginners?

While some shrimp, like Amano (Caridina multidentata) and cherry shrimp (Neocaridina davidi), are relatively easy to take care of, you have to choose tank mates very carefully, and shrimp are generally pretty sensitive to changes in water chemistry. They like stable, established tanks. Shrimp owners have to keep an eye on the amount of minerals present in the water to prevent fatal molting issues. Due to the advanced nature of setting up a shrimp tank, I have excluded shrimp from this list, although they are one of the most low-maintenance aquatic pets you can have once their tank is set up properly.

Why are neon tetras not good for beginners?

Neon tetras are one of the most popular fish for freshwater aquariums. However, despite their wide availability, they are surprisingly sensitive. They also have a disease named after them–Neon Tetra Disease. It is highly contagious, and there is no cure. They do best in stable, established setups after a quarantine period. Their sensitivity to sudden change and susceptibility to disease disqualify them from being beginner-friendly aquarium fish.

Why are otocinclus not good for beginners?

Otocinclus (aka otos or “dwarf sucker mouth catfish”) are small, schooling, algae-eating catfish that only get to be about 2 inches (5 cm) long. Because of their small size, they seem like a great algae eater for smaller tanks. However, many otos are wild-caught. They need very stable, established tanks, and they can be very picky with their food. Many will not touch commercial foods like algae wafers. They exclusively eat algae and biofilm (that slimy stuff that covers surfaces in established tanks). Because of their sensitivity to changes in water parameters and their pickiness with their food, I have excluded them from this list.

Conclusion

Beginner-friendly fish come in all shapes, sizes, and temperaments. Whether you want to start small with a single betta fish or dive right into keeping a school of zebra danios, there is a hardy fish for you! While these are fish that are easy to take care of, they still require care and attention from their keepers.

Regardless of the species you choose, make sure to do plenty of research to understand its needs. By consulting your local fish store employees, online forums, and blogs like this one, you can set yourself and your fishies up for success.

Happy fishkeeping!
Beginner Aquarium Mistakes And How To Avoid Them

January 4, 2026
Setting up your first aquarium can be a daunting task. There are so many things you have to worry about. What water is good for fish? Can all fish go together? What if your pH is wrong? Is your tank too big? And most importantly: How do you keep your fish alive? Luckily, many beginner aquarium mistakes can be easily avoided, and keeping aquariums can be a fun, relaxing, and rewarding hobby once you get past the initial setup.

To help you get started, I’ve created this list of beginner aquarium mistakes that arise when setting up the tank. With a little patience and research, you can make sure your fish survive and thrive.
Starting with a tank that is too small

When I worked in a chain pet store, many first-time fish owners wanted to start small for their first aquarium. They would pick up the smallest enclosure they could find, whether it be a three-gallon, a one-gallon, or a critter tote meant for short-term transport only.

“Oh, if the fish lives, we will upgrade!” they would say. “We are just starting out!”

But starting small is setting yourself up for failure. The smaller the volume of water, the faster it gets dirty, and the more difficult it is for the tank to become established. In larger tanks, the waste produced by the fish is diluted by the increased volume.

Larger tanks are actually easier to maintain than small ones.

Don’t be fooled by the betta cups. These fiery fish need more space than you think!

Small tanks are prone to swings in temperature, pH, and levels of nitrogen compounds.

If a small fish dies in a 20-gallon tank, no big deal (okay, it is rather sad). Of course, you should remove the deceased as soon as possible, but it is unlikely to cause a problem right away. If the same fish were to die in a 3-gallon, any other inhabitants are in serious danger. Carcasses, as well as poop and uneaten food, release ammonia as they break down. In a small volume of water, it quickly becomes toxic!

What if your fish tank is too small?

Your fish can become stressed due to poor water quality, lack of room to swim, or no way to get away from tank bullies.

They can also become stunted. As fish grow, they release a hormone into the water. The concentration of the hormone in the water tells them how much room they have, and it will make them stop growing if it gets too high. “A fish only grows to the size of its tank,” but it will be dealing with things like organ damage, deformities, and a weakened immune system. Purposely stunting a fish is cruel and will substantially shorten its lifespan.

My 75-gallon aquarium with its single inhabitant: an albino tiger Oscar named Fishy. Fishy is nearly 5 years old!

So, when selecting your first tank, choose a size that provides a stable environment and that can support the species you want to keep–long-term–and avoid one of the most common beginner aquarium mistakes.

Using soap

Anything you put into your aquarium should be rinsed in plain tap water before you use it. This includes most substrates, decor, and even your filter (only if it is new!). This removes any dust or debris that could harm your fish or, at the very least, make the water cloudy.

Do NOT use soap or ANY OTHER CHEMICAL with anything that will come into contact with your fish!

According to Dawn’s commercials, it is a great soap to use if you stumble upon a baby duck covered in oil. It is toxic to fish, and they will die if they come into contact with it.

“But what if I rinse it really, really well?”

You can never be sure you got it all. Just don’t use soap.

I’ve had people come in mere hours after I had sold them fish, wondering why they all died. I tested the water, and it was pristine! No ammonia or nitrites. PH was within an acceptable range. But you know what doesn’t show up on those little test strips? Soap. The truth was uncovered after some questioning, and now my customers knew why their 55-gallon tank became a goldfish graveyard.

Cleaning the tank or supplies with soap is one of the most disastrous beginner aquarium mistakes that can result in the death of an entire tank.

Skipping dechlorinator

Most municipal water supplies contain just a tiny bit of chlorine. Just a taste. It helps keep the water safe for us to drink because it kills bacteria. However, it also kills fish.

Chlorine damages fishes’ gills on a cellular level, and then they slowly suffocate.

If you are on city water, you must use a dechlorinator (also known as a water conditioner). It binds to the chlorine and makes tap water safe for fish. Some brands also bind to heavy metals (like lead, manganese, arsenic, etc.) and others temporarily detoxify nitrogen compounds. Skipping dechlorinator is one of the deadliest beginner aquarium mistakes.

Can’t you just let the water sit for 24 hours to get rid of the chlorine?

Sure! But not all of the nasties may evaporate. Tap water also may contain chloramines, which are equally toxic to fish and do not easily evaporate. The easiest and fastest way to remove chloramines from tap water for an aquarium is to use a dechlorinator.

A variety of water conditioners are available at your local pet store.

In addition, water conditioners work instantly, so you can add the water to your tank immediately, provided it is the appropriate temperature.

I use a Hygger water changer for my tank maintenance, and I dechlorinate the water as it pours into the tank, straight from the sink, and I have had no issues thus far. I use Seachem Prime, and although it is stinky, it works wonderfully.

Remember: use a dechlorinator anytime you are adding water to your tank, whether you are setting it up for the first time, doing a water change, or just topping it off.

Using distilled water

If you don’t want to use a dechlorinator, using distilled (or RO) water seems like a good idea. It’s readily available, and many grocery stores have refill stations where you can get that beautiful, pristine water for relatively low cost.

However, distilled water by itself is a poor choice for aquariums, and using it will likely result in fish death.

Why is distilled water bad for fish?

The main reason is that it lacks minerals. All fish, even those from soft-water environments, need some minerals in their water. Water tends to move from areas of low salt concentration to areas of high salt concentration.

Distilled water doesn’t have any salts or minerals, but your fish is full of them. So, where does the water go? Into the fish. This can lead to all sorts of not-awesome things, including organ failure and death, as water enters your fish’s cells and causes them to swell. Using distilled water impacts your fish’s ability to osmoregulate, or control the balance of salts, electrolytes, and water within their system.

In addition, distilled water is prone to pH swings because it lacks buffers (like carbonates) that keep the pH stable, making it unsafe for our sensitive fish friends.

Not using a filter

Fish need a filter because it provides three crucial things: water movement, oxygenation, and a place for beneficial bacteria to grow. Setting up an aquarium without a filter is one of the most detrimental beginner aquarium mistakes, one that can quickly result in your fishes’ demise.

Water Movement

Why is water movement important in an aquarium? It prevents stagnant spots and helps stabilize water temperature, ensuring that the temp is uniform throughout the aquarium.

Most common aquarium fish (like guppies, tetras, gouramis, and angelfish) benefit from having their water in the mid-upper seventies. In many parts of the world, this requires a heater. The filter will help circulate the warm water throughout the tank, ensuring the heater works properly and your fishies have a stable environment.

Water movement also helps prevent the oily looking film that develops on the surface of stagnant water, which can prevent good gas exchange.

Oxygenation

Another reason that filters are important is that they help oxygenate the water. Fish need oxygen in the water to breathe, just like we need it in our air. Without oxygen in the water, your fish may appear to gasp for breath, often gathering at the surface of the water as they struggle to breathe.

A home for beneficial bacteria

The filter on your aquarium is also the primary home for the beneficial bacteria that your fish need to survive. This good bacteria is also found in the substrate and on your plants and decor. Having a filter helps prevent a tank crash by being a refuge for all of your good bacteria. Without one, your tank is more prone to things like ammonia spikes–which can kill your fish.

Adding fish too soon

Another very common beginner mistake when starting an aquarium is adding fish right away. When it comes to keeping fish, patience is a virtue.

You’ve just set up your tank—it has all of its decor, the filter is running, and you’ve added the last little bit of water. It can be tempting to run back to the store and grab your fish. Or perhaps you bought the fish at the same time you bought the tank.

But here’s the thing: new tanks are unstable.

When you first fill up the tank, the water temperature may be all over the place. Warm water rises to the top, and cold water sinks to the bottom. As the fish swim along, they may be fatally shocked when they venture into a pocket of ice-cold water. Allowing your tank to run for a couple of days allows everything to settle and the temperature to stabilize.

Letting your tank run for a bit also lets you make sure that your filter and heater are working correctly and gives you some time to watch for potential leaks.

At minimum, you should let the tank run for 2-3 days before adding your first fish.

Ideally, you will establish the nitrogen cycle before adding your fish. It can take over a month, but it gives your fish the best chance at survival. A fish-in cycle is possible, but it can be rough on the fish as they must cope with tumultuous water parameters.

I recommend a fishless cycle, but fish-in cycles can be performed with plenty of water changes and dosing of certain water conditioners like Seachem Prime, which temporarily detoxify ammonia and other nasties.

Adding too many fish at once

Another beginner aquarium mistake is adding too many fish at once when setting up the tank. They want to fully stock their tank right away. While having a full, lively tank is every aquarist’s dream, it should be your final product, not your first step.

Feeder fish tanks are overstocked and should not be your standard for a healthy aquarium.

When setting up your tank, you should add a few hardy fish at a time, especially if it is uncycled. If you have undergone a full fishless cycle and you know your tank can process the ammonia that your new fish will produce, your initial stocking can be heavier.

Unfortunately, many beginners don’t cycle their tanks ahead of time. They fully stock (or even overstock) their tank right away, and come back a few days later with the tiny bodies.

Stock your tank no more than halfway when adding your fish for the first time. The fewer fish you add, the better. After a few weeks, you can add a few more fish. Slow and steady wins the race!

Keeping incompatible species

Believe it or not, not all fish can live together. Mixing incompatible fish can be one of the most traumatic beginner aquarium mistakes. Even if they are the same size, share a temperature or geographic range, or just look really, really good together, you have to take into account the aggression level of each species.

Understanding fish temperaments

Fish temperaments range from “so chill that you can put them with anything” to “will kill anything that moves.” Fish are typically classified as community/peaceful, semi-aggressive, and aggressive. When setting up your first aquarium, you should make sure that your inhabitants have a similar temperament.

Beginner aquarists should stick to community or semi-aggressive fish, although the latter requires more caution and research.

Bettas (Betta splendens) are highly aggressive toward each other and often other fish. Choose tank mates with care.

Exceptions within a group

Within each class, there is some variation. While most tetras are considered peaceful, they can act semi-aggressively if they are not kept in a group. Livebearers (mollies, platies, guppies, and swordtails) are also considered peaceful, but an improper ratio of males to females can result in relentless bullying.

In addition, not all fish within a class are compatible. For example, tiger barbs and angelfish are both considered semi-aggressive, but they shouldn’t be kept together. Tiger barbs are notorious fin-nippers, and the long-finned angelfish is an easy target.

Mixing temperaments

Can you keep semi-aggressive fish in a community tank? Absolutely! I’ve kept angelfish with platies, corydora catfish, and various tetras. Gouramis make another good addition to a community tank. Some semi-aggressive fish can even be kept with aggressive ones, and some fish transcend boundaries entirely. Take the pleco family, for example. They live with many types of fish, from guppies to Oscars, as long as the tank is large enough to accommodate them.

What happens if you keep a peaceful fish with one that is highly aggressive? Violence. The docile fish will not be able to hold its own. While there are exceptions to every rule, and not every aggressive fish will be bloodthirsty, I strongly recommend beginners do not experiment with tiny fish lives.

Not acclimating your fish

When you bring home your new fish, you can’t just dump them into the tank. They must be slowly acclimated to the temperature. Even if the fish store’s tank is exactly the same temperature as your own, the temperature of the bag likely changed during transport.

How do you acclimate new fish? Simply float them (in their transport bag) for 15-20 minutes. This will make the temperature of the water in the bag the same as the water in the tank.

When that is complete, your fish are ready to be released!

I recommend dumping the bag’s contents through a net, holding the net over a bucket, and then dropping the fish in the tank. Avoid getting the water from the store into your tank. This lessens (though it doesn’t eliminate) the chances that you will introduce disease into your tank.

If the species you are keeping are very sensitive, or if your water is very different from the water the fish came in, a more extensive acclimation process may be required.

In most cases, though, temperature acclimation is enough; it’s a fast and easy way to avoid one of the most common beginner aquarium mistakes!

Not keeping tank at the proper temperature

Not all fish will thrive at room temperature. Some need heaters. Some like it cooler. A couple of common beginner aquarium mistakes are not researching the temperature required for their chosen species and keeping fish with wildly different needs together.

Why temperature matters

What happens if the tank is too cold? Fish may become lethargic, be more susceptible to disease, or stop eating.

On the other hand, tanks that are too warm may not contain enough oxygen in the water. Higher temperatures also speed up the metabolism of fish, essentially putting their lives on fast forward. They grow and age more quickly, potentially leading to an early demise.

How do you know if your fish need a heater?

Research, research, research! A quick Google search will tell you the temperature requirements for your species.

Many popular species—like guppies, platies, tetras, mollies, angelfish, corydoras, and barbs—typically need a heater, preferring their water in the mid-to-upper 70s. Goldfish, rosy red minnows, and white clouds like it cooler, closer to 70.

Depending on your country’s climate, you may not need a heater, even for tropical species. Letting your tank run for a few days before adding fish is the perfect chance to plop a thermometer in your aquarium to see how the ambient temperature affects your tank’s temp.

Chasing perfect parameters

I’ve lost count of the concerned fish owners that ask me, “My tank’s pH is a little high…. what should I do?” They pick up those pH-lowering or stabilizing chemicals. However, they usually do more harm than good.

Most common fish are fine at any pH from high-6 to low-8. Problems arise when you chase an “ideal” pH; rapid swings can stress your fish.

Think about it: you have to dose the product slowly so that it doesn’t stress out your fish. Then, when you reach an ideal pH, you have to dose all of the new water that you put into your tank. What if you forget? And what about evaporation? And the natural tendency of tanks to become more acidic over time?

Using chemicals to artificially change pH or other parameters in your tank may stress your fish. For many species, stability is more important than the “ideal.”

If you feel it is necessary to change your water chemistry, look into natural, slow-acting methods. For example, top off your tank with distilled water to lower the hardness. Add crushed coral to raise your hardness and pH. Peat moss, driftwood, and other botanicals will gently lower your pH.

Conclusion

As a beginner aquarium keeper, you will make beginner aquarium mistakes. I’ve made too many to count! It is inevitable, and an important part of learning. Of course, we are dealing with living creatures, so we want to minimize our errors for their sakes.

I hope this list of mistakes that beginners make when setting up an aquarium has shed some light on the process of starting a new tank and that it made you feel a little bit more comfortable knowing what you should and should not do.

Happy fishkeeping!