How Many (What) Fish Can Go in A 20 Gallon Fish Tank

How Many (What) Fish Can Go in A 20 Gallon Fish Tank

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A 20-gallon fish tank is an ideal aquarium size for the not very experienced aquarist, but one that has kept fish long enough to want something large than a 10-gallon.

In a 20-gallon, it’s possible to keep a wide variety of tropical fishes, not to mention species with bigger overall body size, and even have exotic mixes and stunning schools of small-bodies fishes.

That said, please note that depending on the keep, a 20-gallon long may hold more livestock than a regular 20-gal making it the better option. While in other instances, a 20-gallon tall is best like when maintaining fish with odd shapes like angels.

Below is a list of tropical fishes you can keep. Usually, the rule of thumb is an inch of fish for every gallon of water, which means you can have as many as 15 one-inch fishes and up to 6 2.5 inch fishes in a 20-gallon aquarium.

In a properly setup 20-gallon, you can even have some of the most popular tropical fish such as fancy-goldfish, betta, mollies, platies, danios, rasboras, barbs, small-gouramis, dwarf cichlids, cories, small-catfish, and even schooling fishes, like tetras.

Discussed below is how to stock the popular species from this list.

What are Good Fish For A 20-Gallon Fish Tank

Most species outlined in the list above are good candidates for a 20-gallon fish tank, though some do best in slightly bigger tanks, while others like ottos and betta will fit even in smaller (10-gallon) aquariums.

From experience, the best fishes to keep in a 20-gallon include livebearers (guppies, mollies, platys), small loaches, plecos, and catfish (ottos, cories, bushynose, kuhli loach), fancy goldfish, smaller barbs (barbs, gold), schooling fishes (neon tetras), dwarf gouramis, danios, and dwarf cichlids (blue rams, rainbow kribs, Apistos).

Livebearers in A 20-Gallon Fish Tank

Of all tropical fishes kept in aquariums, livebearers are almost always suited for a 20-gallon tank. Both in the level of care and size of the fishes.

In terms of size, livebearers range between 1.4 inches and 5.5 inches, with swordtails being the larger of the four and fancy guppies being on the lesser end. As such, more fancy guppies (8 to 10) will fit in your 20-gallon fish tanks and only a pair of swordtails.

Reagarding the care and maintenance, with a 20-gallon, you should be able to take anything the livebearers throw at you.

They are not as easy to keep as Betta, but they also do not compare to bigger fishes like Africa cichlids and, Central American cichlids, and South American cichlids such as Angels, and Discus.

Having said that, if you decide to go with livebearers in your 20-gallon, I suggest your try keeping guppies and platys first, particularly if you have limited experience since they grow smaller and have a lighter bioload.

Only go for mollies when you have more experience keeping ornamental fish.

Also, note that swordtails and larger mollies like the sailfin might need to be relocated once they attain maximum size; aggression levels go up as well when larger livebearers are kept in small space.

How Many Guppies in A 20-gallon

You can have one guppy for every 2 gallons of water you have, meaning a 20 gallons aquarium can hold up to 10 individuals.

Even so, to ensure every fish has enough swimming space, especially if you plan on adding plants and other decorations or breeding your fish in the tank, I recommend going with between 6 and 8 individuals.

A group of between 6 and 8 is also ideal if you plan on having your guppies with other tankmates such other livebearers or bottom-dwellers.

How Many Platys in A 20 Gallon

Like guppies, platys are not overly large fish, so you can keep up to 10 individuals in a 20-gallon fish tank. A group anywhere between 8 and 10 is optimal since the species are happy fishes that seem to enjoy being in large groups.

Ideally, you want to keep more females than males in a ratio of 1:3, more so if you intend on breeding your school. So if you have 8 platys, 6 should be females and 2 males.

But remember the number will vary if you intend on keeping your platys with other fish, plus note that livebearers are sensitive about filtration, so make sure you have a dependable unit.

How Many Mollies in A 20 Gallon

As I mentioned before, mollies will live in a 20-gallon, albeit other livebearers (platys, guppies) will do better than them. Moreover, you do not want to keep larger breeds like sailfins in this size aquarium.

If you must, I recommend adding only two mollies in a 20-gallon fish tank. In case you feel your fish tank is too empty and needs a little more action in there, you can pair them with a school of tiny fishes like neon tetras.

I’m sure you already know mollies prefer hard water with a little bit of salinity and might be concerned about pairing them with neon tetras. Rest assured, you can add some salt to your fish tank without causing much discomfort to your neons.

How Many Swordtails in A 20 Gallon

Swordtails, like mollies, tend to lean more toward the larger sized livebearers size. As such, you can only keep a pair (max 3) in a 20-gallon fish tank.

Luckily, they do well with tiny schooling fish, albeit preferring moderately alkaline water, so you can add them with a school of neon tetras if you desire more activity in your fish tank.

However, please note that swordtails can reach 5.5 inches in size and produce quite a sizeable bioload, so consider relocating them if they become too big for your 20-gallon.

Catfish, Loaches, and Plecos For A 20-Gallon

Away from livebearers, which mostly occupy the middle and top levels of a fish tank, a couple of bottom-dwelling fish will also fit in your 20-gallon aquarium.

Notably, cory catfish are well sized for a 20-gallon, same as bristlenose plecos. Both species are native to South America and are reasonably easy to maintain and care for.

In case you want an even smaller fish, the dwarf sucker catfish (also called Otocinclus) is another South American bottom-dwelling species to choose from.

Kuhli loach will also fit in a 20 gallon and ideal when you want something unique, away from your regular catfish and plecos. It’s an interesting small-ill-like fish native to Indonesia and the Malay Peninsula.

How Many Cories in A 20-Gallon

Up to 4 cory catfish (1 in every gallon of water ) can go in a 20-gallon fish tank, but note there are several species of the same family, some of which may grow bigger and some fragile than others.

You can have more pygmy cories in a 20-gallon as opposed to skunk cory since they are smaller and produce a lighter bioload. Also, if you have every inch of your substrate covered with stem plants, you won’t be able to keep as many individuals as you would want.

Of all cory catfish types I would recommend keeping the pygmy, albino, skunk, bronze, emerald, and Sterbie species in a 20 gallon since they are small and hardy and will survive even in less than ideal setting.

Julii and other lesser know (or available) species will also fit in your 20 gallons. But because they are not well explored in the aquarium setting, it’s best to keep them in a bigger fish tank where the situation is easier to manage.

One other thing to note when keeping cories is they do best in groups, meaning you may want a bigger fish tank if you intend to add your with other fishes.

How Many Bristlenose Plecos in A 20 Gallon

The bristlenose pleco is one of the smallest aquarium catfish and will grow up to an average of 3 to 5 inches.

Depending on what fish you keep with your bushynose, you can have one individual in a 20-gallon tank, preferably longer as opposed to a tall aquarium.

Because they produce a lot of waste, try companion your bristlenose with tankmates that have a lighter bioload to reduce the cleaning and maintenance hassle.

You also do not want to keep a bristlenose pleco in such a small space if you have no know-how keeping tropical fish. Instead, go for a 30-gallon fish tank for a fitter fish keeping experience.

How Many Dwarf Sucker (Otocinclus) Catfish in A 20 Gallon Fish Tank

Otocinclus catfish are social fish, living in shoals of thousands in the wild. As such, you’ll want to keep at least 6 in your fish tank.

Due to their small body size, the 6 individuals will fit even in a small 10-gallon tank, with up to 10 individuals being optimal in a 20-gallon.

You may even want to have as many as 15 Otos, with a lesser number only desirable if you intend on maintaining them with tankmates.

Dwarf suckers are an ideal alternative to bristlenose pleco in a 20-gallon aquarium, particularly for newer fish keepers looking to have a small bottom feeder that will feast on algae.

How Many Kuhli Loaches in A 20 Gallon

Each pair of kuhli loach require a minimum of 15 to 20 gallons of water, hence the most ideal number to add to your 20-gallon aquarium.

The fish can grow up to 4 inches, but they’re very peaceful and don’t require a lot of extra space for turf forming.

However, one thing to remember is that kuhli loaches quite often sift and bury themselves in the substrate, meaning a sandy tank base is paramount.

Moreover, they are nocturnal, incredibly shy, and can be very reclusive. When startled, they dart underneath tank ornaments or bury itself if fine gravel or sandy substrate is present.

Fancy Goldfish in A 20 Gallon

Arguably one of the most commonly kept ornamental fish in aquariums, goldfish has over the year suffered the wrath of living in small spaces.

I think I’ve even run out of count the number of times I’ve seen or heard of a goldfish being raised in a bowl.

What most of these hobbyists fail to understand is that a fully grown common goldie can top 11 inches, while the smaller fancy goldfish average 4 to 7 inches making them only suitable for a 20-gallon tank or larger.

How Many Fancy Goldfish in A 20 Gallon Fish Tank

First off, let me start by stating that most goldfish continue growing for most of their life, meaning they are technically not to be kept in a fish tank. Even so, there are so popular all over the world, it would be absurd to ask you not to get one.

That said, most fancy goldfish bred in captivity average between 1 and 4 inches, meaning a single individual will comfortably live in a 20-gallon aquarium.

But if you want to keep more than one goldie, as usually is the case, you may need to get a bigger fish tank. You should allow an extra 10-gallons of water for every goldfish you add to your aquarium.

Another thing to consider is that goldfish produce a lot of waste, which is not desirable in smaller tanks unless you have a considerably powerful filter.

The recommended tank size for goldfish depends on the fish you have. Ideally, fancy goldfish will live Ok in a 3-Feet long tank with an overall volume of 20-gallons or more when kept singly. Aquariawise

Barbs in A 20 Gallon Fish Tanks

Barbs are a family of tropical fishes native to Asia and commonly kept in aquariums. Same as most groups of fish, they are several species of barbs that vary in size and ease of maintenance.

They are all schooling fish and need to be kept in schools of at least 5 individuals. Thus the size of the fish tank is crucial to ensure your barbs are comfy and thriving.

Small species like cherry and gold barbs can be kept in 10 to 20-gallon aquariums, but larger species like tiger, rosy, and black ruby barbs require a minimum of 30 gallons, and larger types like Deninsonii will need a 55-gallon or more when fully grown.

How Many Cherry Barbs in A 20 Gallon

The smallest recommended tank for cherry barbs is a 20 gallon.

Because like all barbs, cherries are a schooling species, they also need to be kept in groups of at least five.

From experience, the best number for a 20-gallon would be between 6 and 8 cherry barbs, depending on the fish you plan to keep with them.

Each cherry barb will require about 4 to 5 gallons tank space, and find safety in numbers.

How Many Gold Barbs in A 20 Gallon

Gold barbs are equally as stunning as cherries and are quite popular in the aquarium hobby. While cherry barbs bear a striking red hue, golden barbs carry a noteworthy yellow-gold color.

Like you may have already guessed, they are a schooling species that are best kept in a group of 5 individuals or more. As such, you can (and need to) accommodate anywhere from five to 8 gold barbs in a 20-gallon tank.

Gold barbs grow to about 3 inches from tip to tail, and because males are territorial, you should allow 3 gallons of tank space per fish, meaning a 20-gallon will hold 6 to 8 gold barbs.

Schooling Fish in A 20 Gallon Fish Tank

Small schooling fishes are among the best to keep in a tank that’s 20-gallons or less. They occupy a very tiny area of the fish tank, meaning you can maintain a large number or add them with tankmates.

Two of the best schooling fish are neon tetras and white clouds. The neons require an environment typical to most tropical fish, but your minnow will survive even in a cold water aquarium.

How Many Neon Tetras in A 20 Gallon

The rule of thumb while stocking neon tetras is a gallon of water for every inch of fish you have. And since tetras max out at an inch long, your 20-gallon fish tank can accommodate up to 20 individuals.

Even so, if keeping your neons with other tropical fish in your aquarium, you may want to go with just 10 or so individuals.

Also, remember neons are quite sensitive to water quality and should only be added in a fully cycled aquarium.

In terms of the settings, they show an affinity for moderately acidic water, preferably darkened with tannins akin to what they are used to in the wild.

How Many White Clouds in A 20 Gallon

Same as neon tetras, white cloud minnow are incredibly tiny, thus take up limited space in the fish tank. You can have as many as 25 individuals in your 20-gallon, though a lesser number is advisable when maintaining them with other fishes.

As I mentioned before, white clouds are quite adaptable and will live even in cold water, making them good companions for goldfish, zebra danios, and weather loaches.

Danios in A 20 Gallon Fish Tank

Danios are hardy fish that are quite common in fish keeping. They are ideal for beginners because they are easy to maintain and can be readily companioned, not to mention suited for small aquariums like a 20-gallon.

Even so, please note there are several species of danios, and in your 20-gallon, you want to add smaller species that’ll fit. Luckily zebra danios and celestial pearl danios are both well suited and readily available.

How Many Zebra Danios in A 20 Gallon

Zebra danios are schooling fish the same as neon tetras and prefer to be kept in large groups where they are quite active.

Therefore, add at least 6 individuals regardless of the aquarium size you have.

The same rule applied for other schooling fish will still apply to zebra danios, that is, a gallon of water for every inch of fish you have. As such, you can have up to 12 (one and a half inch) in your 20-gallon.

Therfore, two schools of zebra danios, each with 6-members will work, though you may want a single group if you have other fishes in the tank.

How Many Celestial Pearl Danios in A 20 Gallon

Celestial pearl danios, though pricey than Zebras, are really stunning fish that are not too hard to care for and will fit well in your 20-gallon aquarium.

Ideally, up to 25 CPDs will fit in a 20-gallon aquarium, but you may want to keep a lesser number if maintaining them with other fishes.

The fish is adaptable and will survive in many different water conditions, and have a subtle temperament, which is ideal for fish in community aquariums.

If you want to maintain yours with companions, I highly recommend putting them with corydoras catfish, both of which will comfortably fit in your 20-gallon tank.

Gouramis in A 20 Gallon Fish Tank

When looking for colorful aquarium fish, small-sized, easy to keep, and ideal for new aquarists, a few gouramis will most definitely come up.

Most gouramis come in brilliant color, more so on males, and are prized for their ability to be the centerpiece of aquariums. Those with somewhat tiny-bodies are ideal for 20-gallons, companioned with schooling fishes such as tetras.

Two gourami species I would recommend keeping in a 20-gallon tank would be the honey and dwarf gourami because of their small body size and are easy to care for compared to rare types like the licorice and paradise gouramis.

Remember betta are part of the gourami family and fit well in 10 to 20 gallon tanks, though most hobbyists consider them independent from other members.

How Many Honey Gourami in A 20 Gallon

Honeys are more peaceful than others in their family, meaning you can keep more than one without too many aggression issues.

Compared to dwarfs, honey gouramis are less temperamental and are practically saint if the feistiness of betta is anything to go by.

If you choose to go with honey gouramis in your fish tank, I recommend having 3 or 4. A pair is more ideal when thinking of space, but they tend to be very shy and only become much more confident in groups.

Also, try mixing yellow and red ones for a bit of variety.

How Many Dwarf Gouramis For A 20 Gallon

Although dwarf gouramis exhibit the reputable feistiness of the family more than honeys, you should be able to keep up to 3 individuals in a 20-gallon aquarium, even with a school 8 to 10 neons.

Ideally, every inch of your dwarf gourami should have at least a gallon of water, so if you have a 3-inch fish like dwarf gouramis, a 20 gallon will be more than enough for your trio.

One pair of dwarf gouramis with eight neon tetras will even allow some room for some cory cats at the bottom of your fish tank.

Cichlids For A 20 Gallon Fish Tank

I’m sure if you’ve only experienced large Central American and African cichlids or Angels and Discus from South America, you must be wondering how any of these will fit in a 20-gallon fish tank.

Well' turns out there are smaller cichlids species, popularly called dwarf cichlids, that have overall tiny bodies, ideal for aquariums as minute as 20-gallons.

Though most dwarf cichlids as described by aquarist fall in the rams and Apistos family, the term is not accurately defined and can encompass any cichlid between 3 and 3.5 inches in size, including Julidochromis and rainbow Kribs from Africa and Apistos and Rams, which are native to South America.

How Many Julidochromis in A 20 Gallon

Julidochromis are a perfect 3 inch fish for when looking to try your hand in keeping African cichlids. They are engaging with an unusual ability to swim vertically, sideways, and upside-down to stay close to surfaces and hiding spots.

You can keep 3 to 6 Julidochromis in a 20-gallon tank as long as you provide them with enough plant cover, rock work, and caves.

Also, keep in mind that, like most other members of the Cichlidae family, these dwarfs exhibit aggression, albeit at lesser intensities, meaning you need to exercise some caution if you choose to keep them.

How Many German Blue Rams in A 20 Gallon

German blue rams are stunning, excitably colored cichlids that do well in a 20-gallon fish tank or larger. Preferably, add them in a long tank to give your GBRs more floor space since they are bottom-dwelling fish.

You can add a single ram or a pair with other fish such as dwarf cories or tetras in your 20-gallon. Adding some shrimp such as Amanos is fine as well, just make sure they are big enough to not fit in the GBRs mouth.

Lastly, if you want to keep more than one male ram, it’s best to go with at least a 40-gallon, because like all cichlids, they sometimes exhibit territorial and aggressive behavior.

How Many Rainbow Kribs in A 20 Gallon

Kribensis cichlids don’t need a massive tank to stay healthy, but the size of your aquarium could have an effect on their stress levels and happiness.

Ideally, you should put your kribs in a 20 to 30-gallon tank. A pair will fit in your 20-gallon comfortably when kept alone, with the extra space left to tame territorial behavior.

If you must add your rainbow kribs with companions, keep them with tiny schooling fish like tetras or calm bottom-dwellers such as cories.

How Many Apistogramma Cichlids in A 20 Gallon Tank

Apistos are wonderful cichlids for a community tank. They live at the bottom of the tank, so they’ll do well with any species that does not take up valuable floor space from them.

Therefore, a long and wide tank is best to give your Apistogramma their own territory to claim. Thus we also recommend only putting them with tetras, pencil fish, and other species that like to swim in the middle or towards the top of the tank.

Generally, Apistos grow to between 3 and 3.5 inches maximum size and are all native to South American.

Given this size, they only require their tank to be larger than 15 gallons, which places your 20-gallon within their comfort zone.

A pair or trio of Apistogramma will fit fine in a 20-gallon (a gallon for every inch of fish), usually preferring to live in pairs or in a group with one male and two (or more) females.

Non Fish Animals For A 20 Gallon Fish Tank

Apart from fish, there are other aquatic pets ideal for a 20-gallon tank, including amphibians and inverts like shrimp and crabs.

The first, and probably the most intriguing would be axolotl, which is fairly easy to keep. You only need to make sure you have a lid for the tank because these amphibians are escape artists.

Axolotl Tank Size (+Requirements, Care)

At least a 15 to 20-gallon fish tank is recommended for a single axolotl.

Your adult might even fit in a 10-gallon aquarium, but because the amphibians produce a lot of waste, go with a larger tank to help you easily maintain ideal water quality.

Make sure your fish tank is filled to the very top to allow your axolotl more swimming room, but also note they are escape artists. As such, have a lid for your aquarium.

If you want companions for your axolotl, I recommend going with mollies since they are a little too big for the amphibians to eat and are hardy enough to survive the axolotl’s filth.

Freshwater Crabs

Although there are not many fully aquatic freshwater crabs, there are a few candidates suitable for a 20-gallon tank. On average, most reach an adult size of between 1 and 4 inches.

This means your crabs will fit anywhere from a 5-gallon tank, depending on the species you have.

Since most freshwater crabs are omnivores, they will eat snails, shrimp and even pose a threat to tiny tropical fish, so consider companions that are bigger and meaner than they are.

Shrimp and Snails

Shrimp and snails are some of the most popular aquatic pets after tropical fish. They are valued for their small sizes, ease of maintenance, and overall calm demeanor.

Most shrimp and snail species will live with fish as long as they are large enough not to fit in the fish’s mouth.

Any tank larger than 5-gallons will accommodate a school of snails or shrimp comfortably, so will your 20-gallon tank even with fish in it.

That said, please note that most freshwater inverts are sensitive to chemicals in water, including residue from copper-based medicines. As such, ensure you keep your tank as pristine as possible.

Thats all for this post.

Happy fish 🐠🦐 keeping.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

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