Best Fish for a 20 Gallon Tank: 21 Great Choices That Actually Work

Last Updated: May 19, 2026

Twenty gallons is where the hobby gets interesting. It’s big enough to run a real community, stable enough that one missed water change won’t crash everything, and small enough that most people can actually fit it in their home. After 25 years in this hobby and time managing fish stores, I’ve set up more 20-gallon community tanks than I can count. A well-stocked 20-gallon is more impressive than a 75-gallon done wrong.

Most people treat the 20-gallon as a starter tank. The ones who stock it right never want to move up.

What People Get Wrong About 20-Gallon Tanks

The most common mistake I see: treating the 20-long and 20-high as the same tank. They hold the same water, but they are not the same tank.

The 20-long (30 inches x 12 inches) gives you a 360 square inch footprint. The 20-high (24 inches x 12 inches) gives you 288 square inches. That’s a 25% reduction in floor space. For bottom-dwelling fish like corydoras, for territorial dwarf cichlids that need their own zones, and for active schooling fish that need horizontal run room, that difference matters a lot.

The second mistake: stocking based on what looks good at the store, not what works together long-term. A 20-gallon has limits. Push those limits with incompatible fish or oversized species, and the problems stack fast: aggression, parameter crashes, sick fish. The list below is built around species that actually work in this size, not just fish that technically survive in it.

The third mistake, and this one costs people fish: not knowing minimum school sizes. Three neon tetras in a 20-gallon is not a school. It’s three stressed fish. A proper school of small tetras needs at least six individuals, and ten to twelve is where they really start behaving naturally and looking the way you imagined when you bought them.

Setup For 20-gallon Aquarium

Before I introduce some excellent freshwater fish for your 20-gallon aquarium, let’s take a few moments to cover some important concepts when setting up a successful community tank.

Why Choose This Aquarium Size

The 20-gallon tank is probably the best all-around choice for a beginner’s community aquarium tank. This tank size offers a number of benefits, including:

• Affordable tank and equipment
• Most homes have enough spare space for a 2 – 2.5 foot tank
• Lightweight enough to be kept on sturdy, level furniture
• Large enough tank to offer some water quality stability but small enough to make water changes easy
• Wide range of stocking options

Long vs High – Which Shape to Choose?

20-gallon aquariums come in two standard shapes, and each one has its own pros and cons.

The 20-gallon long is generally the best choice because it has a larger floor area or ‘footprint’. This means it can house more bottom-dwelling fish and plants.

However, the 20-gallon high takes up less floor space in your home, so this option is better if you have limited free space.

Stocking Your Aquarium – How Many is Too Many??

This is the age-old question in the aquarium hobby because many fishkeepers want to keep as many fish as possible. Unfortunately, there is no easy answer, and the safest piece of advice is to understock your aquarium rather than cram your tank.

As a very rough guideline, you could easily keep 10 – 15 small (1-2 inch) fish in a tank of this size with good filtration and regular maintenance. However, maintaining good water conditions becomes more difficult as you add more fish or increase the size of the fish species you keep.

How To Create A Community

Different fish species have different habits and behavior. Some fish need the company of their own species and must be kept in schools. Others are perfectly happy alone, and some are so territorial that keeping them together with their own kind is a recipe for disaster!

Different species use their swimming space in different ways too. Some are very active and swim around in the middle of the tank all day. Others spend most of their time hanging out at the bottom or hiding away in caves.

So how do you safely create a peaceful community tank that just works? There are loads of options out there, but the following example is tried and tested:

• A small group of schooling bottom dwellers like corydoras catfish
• A school of mid-water fish like tetras
• A pair or single centerpiece fish. The ideal centerpiece fish species is peaceful, slightly larger than its tank mates, but not large enough to snack on them.

Of course, each fish species needs to be compatible in terms of their temperature and water parameter needs. Choosing fish species that come from the same natural habitats and areas of the world is a great way to make sure each fish will be comfortable.

Best Fish For 20 Gallon Tanks

Now that you know a little more about setting up an awesome 20-gallon aquarium, let’s move on to the real stars of the show – the fish!

There are so many amazing fish that can be housed in a 20-gallon tank that choosing a few for a single tank is pretty daunting. Well, look no further – the 21 species in this list are all perfect choices! We got a video from our YouTube Channel below and further details in our blog!

Everything you need to know about each species is included, too, so you can pick out your schooling species, bottom-dwellers, and centerpiece fish with ease.

Let’s meet some fish!

1. Betta

• Scientific name: Betta splendens
• Care level: Easy
• Minimum tank size: 5 gallons
• Temperament: Semi-aggressive
• Adult fish size: 2.5 inches
• Origin: Southeast Asia
• Temperature: 75 – 80 °F
• pH: 6.8 – 7.5
• Diet: Carnivorous
• Swim Level: Top & Mid-water
• Type: Centerpiece fish

The betta fish or Siamese fighting fish makes an ideal centerpiece fish for a 20-gallon tank. You’ve probably heard how aggressive these fish can be, and while that’s true when keeping more than one, they are usually very safe with other peaceful fish species.

2. Rummy Nose Tetra

• Scientific name: Hemigrammus rhodostomus
• Care level: Intermediate
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 2 inches
• Origin: South America
• Temperature: 76 – 80 °F
• pH: 5.5 – 7
• Diet: Omnivorous
• Swim Level: Mid-water
• Type: Schooling fish

The rummy nose tetra is an excellent choice for the midwater of a 20-gallon community tank. These silvery fish really stand out with their black and white striped tails and bright red faces. They are true schooling fish so pick up a group of at least six for an awesome display.

3. Dwarf Gourami

• Scientific name: Trichogaster lalius
• Care level: Easy
• Minimum tank size: 10 gallons
• Temperament: Peaceful
• Adult size: 2.5 – 3.5 inches
• Origin: Pakistan, Bangladesh, India
• Temperature: 72 – 82 °F
• pH: 6 – 8
• Diet: Omnivore
• Swim Level: Top & Mid-water
• Type: Centerpiece fish

The Dwarf Gourami is a beautiful tropical fish with a deep body shape and interesting hair-like pelvic fins. These fish are available in a few color morphs like the stunning powder blue gourami and others with varying shades of neon blue and red.

Dwarf Gouramis are great centerpiece fish, but they will be happiest if kept in a pair. You could keep two females together but avoid two males as they will fight with each other.

4. Cory Catfish

• Scientific name: Corydoras spp.
• Care level: Easy
• Minimum tank size: 20 gallons for most species
• Temperament: Peaceful
• Adult size: 1 – 3 inches
• Origin: South America
• Temperature: Species-dependent. Most thrive in 74 – 80 °F
• pH: 7 – 8
• Diet: Omnivorous
• Swim Level: Bottom
• Type: Schooling fish

Cory catfish don’t have the intense colors of the other species on this list, but they are super interesting and peaceful fish. There are many different species available in the aquarium hobby, but most will do great if kept in a small school in a tropical community aquarium.

Corydoras are bottom-dwellers, but don’t be surprised to see them shoot up to the surface for a breath of air every now and then. These fish will feed on leftover food from the midwater fish above, but they also need a good quality sinking food for a balanced diet.

5. Apistogrammas

• Scientific name: Apistogramma spp.
• Care level: Intermediate to advanced
• Minimum tank size: 10 gallons
• Temperament: Peaceful – semi-aggressive
• Adult size: 2 – 3 inches
• Origin: South America
• Temperature: 74 – 80 °F
• pH: 6 – 7
• Diet: Omnivorous
• Swim Level: Bottom
• Type: Centerpiece fish

Apistogrammas are South American dwarf cichlids that have amazing colors and great personalities. There are many species available in the hobby, but the cockatoo dwarf apistogramma (A. cacatuoides) is one of the most popular and easy to find.

These tiny cichlids are available in many bright color morphs and they make great centerpiece fish in a 20-gallon long or high. These little guys can be territorial, so stick to just one male and female to keep the peace.

6. Zebra Danios

• Scientific name: Brachydanio rerio
• Care level: Easy
• Minimum tank size: 10 gallons
• Temperament: Peaceful
• Adult size: 1.5 – 2 inches
• Origin: India
• Temperature: 64 – 77 °F
• pH: 7 – 7.8
• Diet: Carnivorous
• Swim Level: Top & Mid-water
• Type: Schooling fish or Centerpiece fish

Zebra Danios are excellent community fish if you enjoy loads of movement in your tank. This active and peaceful species is very affordable, so you won’t break the bank by buying a nice school of 6 to 8. Zebra danios are super-tough too, so they are the perfect choice for novice fish keepers.

7. Bolivian Ram

• Scientific name: Mikrogeophagus altispinosus
• Care level: Intermediate
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 2.5 – 3 inches
• Origin: Brazil and Bolivia
• Temperature: 75 – 82 °F
• pH: 6 – 7.5
• Diet: Omnivorous
• Swim Level: Mid-water & Bottom
• Type: Centerpiece fish

The Bolivian ram is a stunning centerpiece species that is right at home in a 20-gallon tank. However, this is the smallest tank size for these fish, so a pair is the most you’re going to get away with.

Unlike African cichlids, these beautiful fish are very peaceful fish and they will do best in a well-planted tank with some cozy hiding spots.

8. Ember Tetras

• Scientific name: Hyphessobrycon amandae
• Care level: Easy
• Minimum tank size: 5 gallons
• Temperament: Peaceful
• Adult size: 0.75 inches
• Origin: Brazil
• Temperature: 72 – 82 °F
• pH: 5 – 7
• Diet: Carnivorous
• Swim Level: Mid-water
• Type: Schooling fish

Ember Tetras are a great choice if you’re planning a busy 20-gallon tank with many small fish. With good filtration, you could easily house 12 or more of these tiny fish in the mid-level of the tank and still have room for some bottom dwellers below.

9. Kribensis

• Scientific name: Pelvicachromis pulcher
• Care level: Easy
• Minimum tank size: 20 gallons
• Temperament: Peaceful – semi-aggressive
• Adult size: 3 – 4 inches
• Origin: West Africa
• Temperature: 75 – 81 °F
• pH: 5 – 7.5
• Diet: Omnivorous
• Swim Level: Mid-water & Bottom
• Type: Centerpiece fish

Kribensis are beautiful African cichlids that can be kept in a 20-gallon tank and their bright colors and bold stripes make them awesome centrepiece fish. A pair will even breed in a tank this size, although they can become pretty aggressive when spawning.

Choose hardy, fast-swimming tank mates like the zebra danio that will make your kribs more confident and easily escape them when breeding.

10. Harlequin Rasbora

• Scientific name: Trigonostigma heteromorpha
• Care level: Easy
• Minimum tank size: 10 gallons
• Temperament: Peaceful
• Adult size: 2.5 inches
• Origin: Southeast Asia
• Temperature: 70 – 82 °F
• pH: 5 – 7.5
• Diet: Carnivorous
• Swim Level: Top & Mid-water
• Type: Schooling fish

Harlequin rasboras are always a great choice when setting up community tanks because they combine great colors and a placid nature. These pale orange fish get along perfectly with other peaceful fish and aquarium life, especially in a planted tank.

11. Checkerboard Cichlid

• Scientific name: Dicrossus filamentosus
• Care level: Intermediate
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 3 – 4 inches
• Origin: South America
• Temperature: 79 – 86 °F
• pH: 4.5 – 6.5
• Diet: Omnivorous
• Swim Level: Bottom
• Type: Centerpiece fish

The checkerboard cichlid (video source) is an interesting species that not many fishkeepers know about. However, these streamlined South American cichlids are great for experienced fishkeepers with a 20-gallon tank because they stay small and live peacefully with other tank mates.

These fish are ideal for a blackwater biotope with other species that need soft, acidic water.

12. Cardinal Tetra

• Scientific name: Paracheirodon axelrodi
• Care level: Intermediate
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 1.25 inches
• Origin: South America
• Temperature: 74 – 84 °F
• pH: 4.5 – 6.5
• Diet: Omnivorous
• Swim Level: Top & Mid-water
• Type: Schooling fish

Freshwater fish don’t get much more colorful than the cardinal tetra. These stunning fish are the slightly larger and rarer cousin of the popular neon tetras of the Amazon River Basin.

A school of 6 to 12 cardinal tetras would look amazing in a well-planted fish tank with one or two other peaceful species at the bottom of the tank.

13. Honey Gourami

• Scientific name: Trichogaster chuna
• Care level: Easy
• Minimum tank size: 10 gallons
• Temperament: Peaceful
• Adult size: 2 inches
• Origin: India
• Temperature: 72 – 81 °F
• pH: 6 – 7.5
• Diet: Carnivorous
• Swim Level: Top & Mid-water
• Type: Centerpiece fish

Honey Gouramis are smaller and more peaceful than dwarf gouramis, making them ideal as a centerpiece fish or even a small group. These colorful fish are a great choice for community tanks where they will get along great with schooling species like neon tetras or zebra danios and bottom dwellers like cory catfish.

14. Cherry Barb

• Scientific name: Puntius titteya
• Care level: Easy
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 2 inches
• Origin: Sri Lanka
• Temperature: 72 – 80 °F
• pH: 6 – 8
• Diet: Omnivorous
• Swim Level: Mid-water
• Type: Schooling fish

Cherry Barbs are another excellent community fish for 20-gallon tanks. Their peach-orange color, bold scale pattern, and dark lateral stripe make them mesmerizing schooling fish if kept in a group of at least 6.

This popular species is ideal for an Asian biotope aquarium with bottom dwellers like kuhli loaches and peaceful gouramis.

15. Peacock Gudgeon

• Scientific name: Tateurndina ocellicauda
• Care level: Easy
• Minimum tank size: 15 gallons
• Temperament: Peaceful
• Adult size: 3 inches
• Origin: Papua New Guinea
• Temperature: 72 – 79 °F
• pH: 6.5 – 7.5
• Diet: Carnivorous
• Swim Level: Bottom
• Type: Centerpiece fish

Are you looking for a unique and colorful addition for your twenty-gallon tank? Look no further than the peacock gudgeon! This species is a great choice for the bottom of your tank, especially if you keep them in small group.

These fish are very easy to care for, although they can be fussy eaters at first. They will adapt quickly if you provide plenty of hiding places at the bottom of the tank and feed them live and frozen foods like bloodworms.

16. Guppy

• Scientific name: Poecilia reticulata
• Care level: Easy
• Minimum tank size: 5 gallons
• Temperament: Peaceful
• Adult size: 1.5 – 2.5 inches
• Origin: South America
• Temperature: 63 – 82 °F
• pH: 7 – 8.5
• Diet: Omnivorous
• Swim Level: All levels
• Type: Schooling fish

Fancy guppies are often overlooked because they are so common, but they are an excellent choice for a community tank, especially if you have naturally hard water.

Male guppies are particularly colorful, and their flowing fins really make them stand out in community tanks. Guppies are a favorite fish all over the world thanks to their hardy nature, high activity levels, and ease of care.

17. Splendid Killifish

• Scientific name: Aphyosemion splendopleure
• Care level: Intermediate
• Minimum tank size: 10 gallons
• Temperament: Peaceful, shy
• Adult size: 2 inches
• Origin: West Africa
• Temperature: 72 – 79 °F
• pH: 6 – 7
• Diet: Carnivorous
• Swim Level: Mid-water
• Type: Centerpiece fish

The splendid killifish is another interesting choice for more experienced fish keepers. These shy fish hail from forested streams of West Africa where their natural habitat is always dimly lit.

Keep your splendid killifish in a tank with plenty of live and floating plants or under low lighting to see them at their best.

18. Red Eye Tetra

• Scientific name: Moenkhausia sanctaefilomenae
• Care level: Easy
• Minimum tank size: 20 gallons
• Temperament: Peaceful but active
• Adult size: 2.5 – 3 inches
• Origin: Paraguay, Argentina, Brazil
• Temperature: 73 – 82 °F
• pH: 6 – 7
• Diet: Omnivorous
• Swim Level: Mid-water
• Type: Schooling fish

The red eye tetra is a common and affordable freshwater community fish that is perfect for aquarists who want a slightly larger schooling fish.

These active tetras need fish tanks with plenty of open swimming space, so a 20-gallon long is going to be the best choice. A group of 6 to 8 will bring a flash of silver and red to the middle layers of your tank.

19. German Rams

• Scientific name: Mikrogeophagus ramirezi
• Care level: Intermediate-advanced
• Minimum tank size: 20 gallons
• Temperament: Peaceful
• Adult size: 1.5 inches
• Origin: Venezuela, Brazil, Colombia
• Temperature: 80 – 86 °F
• pH: 5 – 7
• Diet: Omnivorous
• Swim Level: Bottom & Mid-water
• Type: Centerpiece fish

German rams are colorful and confident dwarf cichlids from South America that are available in many breeds and color morphs, including long-finned, golden, and electric blue ram.

These tropical fish require warm conditions and high water quality to thrive, which is why they are generally recommended for more experienced fish keepers. However, with the right diet and care a pair of these stunning centerpiece fish will be the stars of your 20-gallon tank.

20. Celestial Pearl Danio

• Scientific name: Celestichthys margaritatus
• Care level: Intermediate
• Minimum tank size: 10 gallons
• Temperament: Peaceful
• Adult size: 0.75 inches
• Origin: Myanmar
• Temperature: 68 – 78 °F
• pH: 6.5 – 7.5
• Diet: Omnivorous
• Swim Level: Mid-water & Bottom
• Type: Schooling fish

The Celestial pearl danio is a tiny Asian species (also known as leopard danio) that was first discovered less than two decades ago. Since then they have become extremely popular in the aquarium trade for their beautiful colors and markings.

These leopard danios thrive in cooler water, so they aren’t the ideal choice for warm-water tropicals like ram cichlids. Larger mid-water fish often outcompete them at mealtimes, so pick a couple of other peaceful nano species for their tank mates.

21. Black Neon Tetra

• Scientific name: Hyphessobrycon herbertaxelrodi
• Care level: Easy
• Minimum tank size: 15 gallons
• Temperament: Peaceful
• Adult size: 1.5 inches
• Origin: Brazil
• Temperature: 68 – 82°F
• pH: 5 – 7.5
• Diet: Omnivorous
• Swim Level: Top & Mid-water
• Type: Schooling fish

Black neon tetras are active schooling fish from South America that spend most of their time in the middle to upper levels of the aquarium.

These hardy fish are great tankmates for a small group of corydoras and a pair of electric blue rams in a tropical community setup. For the smallest corys, check out the pgymy or panda corydoras.

FAQs

How many fish can I keep in a 20-gallon tank?

It depends on species size and your filtration. A realistic community for a 20-gallon: a school of 8-10 small tetras or rasboras, 4-6 corydoras, and 1-2 centerpiece fish. That’s roughly 14-18 fish, heavily weighted toward small species. Avoid the “inch per gallon” rule entirely. It was never accurate for anything other than the smallest fish in the simplest tanks.

Should I get a 20-gallon long or a 20-gallon high?

Get the 20-long. It has a larger footprint (30 x 12 inches versus 24 x 12 inches), which means more horizontal swimming space, more bottom area for corydoras, and more planting room. The 20-high is a compromise that mainly benefits people who are tight on horizontal space and can accept fewer stocking options.

Can I keep a betta with other fish in a 20-gallon?

Yes, and a 20-gallon is actually a great size for a betta community. Pair a single male betta with peaceful bottom dwellers like corydoras and small mid-water schooling fish like ember tetras or harlequin rasboras. Avoid fin nippers like tiger barbs and avoid other betta males entirely. The extra water volume helps diffuse aggression and gives tank mates escape room.

What fish can’t I keep in a 20-gallon?

Goldfish need more space and different water temperatures. Large cichlids need territory. Oscars, flowerhorns, and similar species will outgrow a 20-gallon before they’re a year old. Angels are borderline: a single angel can work in a 20-gallon long, but a pair will become territorial and stress everything else. When in doubt, look up the adult size and minimum tank recommendation before you buy.

Do I need live plants in a 20-gallon community tank?

Not required, but they make a significant difference. Live plants reduce nitrates between water changes, provide hiding spots that reduce stress and aggression, and make the tank look dramatically better. For a 20-gallon, low-tech plants like java fern, anubias, and cryptocoryne species work with most standard lighting and require no CO2 injection.

What is the best centerpiece fish for a 20-gallon?

For a peaceful planted community, a pair of apistogrammas or a single male betta is hard to beat. For something more personable and hardy, a pair of Bolivian rams works well. For visual impact without aggression, the honey gourami is underrated and underused. Avoid keeping two male dwarf gouramis together: they will fight, and the disease risk from mass-farmed specimens is real.

Final Thoughts

A 20-gallon done right is one of the most satisfying tanks in the hobby. It’s big enough to create real ecosystem dynamics, small enough to stay manageable, and the right size to actually watch fish behavior rather than just see colored shapes moving in the distance.

The 21 species on this list all work. But the tank only comes together when you match species intentionally: fish that share temperature ranges, use different tank zones, and leave each other alone most of the time. Pick your community with that framework in mind, not just by what caught your eye at the fish store.

Choose the right fish. Get the 20-long. Stock it with intention. You’ll build a tank that looks like it was designed by someone who actually knows what they’re doing. Because it will be.

Got a 20-gallon running? Tell us what you’re keeping in the comments below.

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📘 Want to learn more? This article is part of our complete Freshwater Fish Guide: your ultimate resource for freshwater species, care tips, tank setup, and more.

References

• Seriously Fish: Species profiles and care data
• FishBase: Taxonomy and scientific data
• Practical Fishkeeping: Husbandry and care advice