40 Best Fish For Stocking A 20 Gallon Tank – Ideas & Combinations You Can Copy

We decided to look at some of the best fish for a 20-gallon fish tank to help stock the perfect tank. Of the many fish we’ve included in the list, these are the best fish for a 20-gallon tank we could find:

  1. The Best Fish For A 20 Gallon Tank Overall: Tetras or Guppies
  2. Most Unique Fish For A 20 Gallon Tank: Scarlet Badis
  3. Best Big Fish For A 20 Gallon Tank: Blue Ram Cichlid
  4. Best Community Fish For A 20 Gallon Tank: Tetras

Alright, let’s get started:

If you’re going to be setting up and stocking a 20-gallon aquarium, you may be asking a few of the following questions:

  1. How many fish can you keep in a 20-gallon tank?
  2. What are the best fish for a 20-gallon tank?
  3. 20 Gallon stocking ideas
  4. What is the biggest fish you can put in a 20-gallon tank?
  5. Can Goldfish live in a 20-gallon tank?
  6. How many Tetras can I put in a 20-gallon tank?
  7. What other animals can live in a 20-gallon tank?

Overall a 20-gallon tank is a small size tank, so you’ll want to be careful with how many and the types of fish you keep.

If you’re still wondering what you should do?

Good news!

Below we will answer all these questions and even show you some other tiny things that you can fit comfortably in your 20-gallon tank.

Watch this video!

Let’s begin.


Infographic – Best Freshwater Fish For A 20 Gallon Fish Tank

Infographic - 20 gallon fish tank ideas
Infographic – 20-gallon fish tank ideas

Question #1 How many fish can you keep in a 20-gallon tank?

Ah, yup, this question again!

And if I’m honest, it depends!

Seriously though, how many fish can you put in a 20-gallon tank?

A general rule of thumb is you should try to aim for one small fish per gallon of water, and by “small” fish, I mean Tetra-sized fish.

It equates to approximately 1 inch of fish per gallon.

But it’s not always that easy; you can see my thoughts on that here to see what I think.

You should be able to fit about 15-20 small fish in your tank at first, and as the tank matures and you get better at fish keeping. After that, you can maybe keep 20-25 if you don’t mind some work.

However, most beginners do this; they buy a 20-gallon tank and fill it with a few fish without doing a little bit of research.

But you’re not like most people, and you at least asked the question, so good on you.

The problem most beginners don’t realize is that you need to consider a few things like;

  • The size of the fish and growth rate
  • Species of fish
  • Tank mates
  • Their temperament, how aggressive are they?
  • How dirty are they

For example, larger species of Goldfish can grow up to 6″ in size in less than a year.

Can you see a huge 6″ Goldfish living comfortably in a 20-gallon tank?

Maybe, but it’s getting cramped

What if you could find a few examples of fish you could put in your 20-gallon tank?

Well, you’re in luck; that’s what I’ve prepared below.

Further Reading: Best freshwater aquarium fish

Question #2 What are the best fish for a 20-gallon tank?

Below are a few tropical fish species that would make a great addition?

To help, we’ve split them into a few groups:

Community fish

  • Platy
  • Tetras
  • Rasboras
  • Corydoras Catfish
  • Guppies
  • Dwarf Cichlids
  • Shrimp

Schooling fish

  • Small Tetras
  • Rasboras
  • Corydoras Catfish

Aggressive fish

  • Bettas (Siamese fighting fish)

Big fish

  • Dwarf Cichlids
  • Gourami

Hopefully, that was helpful, but if that list wasn’t BIG enough for?

No worries, Cory shares some of his BEST Ideas for your 20 Gallon Aquarium in the video below.

Question #3 What Are Some Good 20 Gallon stocking ideas

Here is the most extensive stocking list for a 20-gallon tank that I could create.

There are 40 fish you can pick from.


  • Cardinal Tetras
  • Ember Tetra
  • Black Neon Tetra
  • Neon Tetras
  • Rosy Tetra
  • Flame Tetra
  • Head and Taillight tetra


  • Lambchop Rasbora
  • Chilli Rasbora
  • Glowlight Rasbora
  • Harlequin Rasboras
  • Least Rasbora
  • Dwarf Rasbora
  • Red Dwarf Rasbora
  • Microrasboras Galaxy


  • Mixed Platies
  • Parrot Platy
  • Red Platy
  • Coral Platy
  • Red Diamond Platy

Female & Male Guppies:

  • Endler Guppies
  • Fancy Guppies


  • Angel Ram Cichlids
  • Electric Blue Ram
  • German Blue Ram
  • Gold Ram Cichlid
  • Apistogramma Borelli Opal


  • Dwarf Gourami
  • Red Dwarf Gourami
  • Sparkling Gourami
  • Honey Gourami

Cory Catfish:

  • Panda Corydoras Catfish
  • Albino Corydoras Catfish
  • Peppered Corydoras Catfish


  • Red Fire shrimp
  • Tiger shrimp
  • Cherry shrimp
  • Amano shrimp


  • Betta Fish
  • Scarlet Badis
  • Dwarf Puffer

If none of the above species are what you’re looking for in terms of fish, well, too bad, that was a lot of work, and maybe you need a larger tank.

Or you can check out one of these articles for more ideas:

That said, a larger tank is easier to maintain and will allow you to keep a more extensive selection of fish.

Centerpiece Fish Ideas

Having a community tank is excellent, but every tank should have that one fish that makes everything come together, that one fish that makes your guest say wow.

These are called centerpiece fish, and if you need a few more ideas, check out our article about the best centerpiece fish for a 20-gallon tank. 

Lastly, if you still need more ideas, here is another excellent video from Aquarium CoOp, where he shares a few FUN Ideas for your 20-gallon Fish Tank.

What Are Some Good Fish Combinations For A 20 Gallon Tank?

When stocking your 20-gallon tank, it’s good to try to have one or two larger “Centerpiece” fish and fill in the rest with a school of smaller fish and a few peaceful bottom dwellers like shrimp or catfish.

It’s really up to you!

Adding a school of fish to a 20-gallon tank can be an exciting and rewarding experience. Find the perfect species that will thrive in a smaller environment while still displaying the captivating behaviors of schooling fish. Read our comprehensive guide on the best schooling fish for 20-gallon tank and create a lively, dynamic centerpiece for your home or office today.

Here are a few suggestions you can try:

Combo-One: The Betta Tank

  • 1 Betta Fish
  • 10-15 Harlequin rasbora
  • 4 Panda Corydoras Catfish

Combo-Two: The Ram Tank

  • One pair (m/f) Electric Blue Rams
  • 10-15 Ember Tetra
  • 4-6 Albino Corydoras Catfish

Combo-Three: The Gourami Tank

  • One pair (m/f) Dwarf Gourami
  • 10-15 Glowlight rasbora
  • 8-10 Cherry Shrimp

Lastly, if you’re a beginner, you could try setting up a low-tech planted tank with a few live aquatic plants.

This will help keep the water quality in check and prevent spiking.

Some great beginner plants are;

In a 20-gallon tank, try;

  • 4-6 x Java Fern
  • 8 x Anubias
  • 4-6 x Java Moss Ball

Overall, a twenty-gallon tank is ideal for a beginner to start a small community tank!

And always remember, It’s important to understand the nitrogen cycle and how to maintain healthy water conditions for your fish.

Question #4 What is the biggest fish you can put in a 20-gallon tank?

On average, a 20-gallon tank is approx 24 – 30″ long and about 12″ wide, depending on if you have a standard or long tank.

Knowing this, if you have fish that is 6″ long when they reach adult size, then it only has 18″ to swim back and forth and will only have 6″ in tank width to turn around. So effectively, your 20 gallon is now only 18 “x6”.

That’s about the size of a shoebox, with not much room.

Personally, the biggest fish I would keep in a 20-gallon would be about 3-4″ full-grown.

Question #5 Can Goldfish live in a 20-gallon tank?

You’ll notice that the Goldfish was not one of them out of all the fish I listed above. Therefore, the smallest tank size you should keep a goldfish is a 20-gallon tank.

That said, that would be the smallest, and I wouldn’t recommend doing the minimum. Seriously, they poop a lot and grow way too big, don’t do it! Seriously don’t.

Question #6 How many tetras can I put in a 20-gallon tank?

When determining how many fish you can keep in any size tank, one of the most common rules is the one inch of fish per gallon rule.

Using this rule, you would be able to keep about 20 small tetras in your 20-gallon aquarium.

While this is a good starting point and might work for much smaller community fish such as tetras, it shouldn’t be applied to larger and messier fish like Oscars, Cichlids, and Goldfish.

Other methods to determine stocking levels include;

  • Fish weight per volume
  • Fish length to filter capacity
  • Fish length per volume or surface area

All these methods have their flaws when considering large fish, messy fish, or fish with particular needs. The best thing to do is to understand each fish you intend to keep in your 20-gallon tank and their specific needs, where they are from, and if your tank has filtration, live plants, and any other fish.

Question #7 What other animals can live in a 20-gallon tank?

While fish are likely the most popular fish you can keep in a 20-gallon tank, there are a variety of mammals, snakes, lizards, and amphibians that you could stay in a 20-gallon tank.

For more information, check out this article about other animals that can live in a 20-gallon tank.

Here are a few more articles you will find helpful when looking at stocking some smaller-sized tanks.

Best Fish For Stocking A 20 Gallon Tank Ideas & Combinations You Can Copy
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