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

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With that out of the way.

We decided to take a closer look at some of the best fish for a 20 gallon 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 TankDwarf Cichlids
  4. Best Community Fish For A 20 Gallon Tank: Glowlight Tetra

Alright let’s get started:

If you’re going to be setting up and stocking a 20 gallon tank 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 mid-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.

Let’s begin.

A Few 20 Gallon Fish Tank Ideas

Infographic – 20 Gallon Fish Tank Ideas

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?

Well, you should try to aim for one small fish per gallon of water, and by “small” fish, I mean like 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.

That said, 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. You can maybe keep 20-25 if you don’t mind some work.

However, this is what most beginners do; 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 growth rate for your fish
  • Their temperament, how aggressive are they?
  • How dirty are they

For example, a small 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

That said, 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 of the Best Fish Species for a 20 Gallon Fish Tank?

  • Small tetra species
  • Cichlids
  • Small Rasboras
  • Dwarf Gourami species
  • Bettas (Siamese fighting fish)
  • Fancy Guppies
  • Shrimps

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

Community fish

  • Platy
  • Tetra
  • Rasbora
  • Corydoras Catfish
  • Guppies
  • Dwarf Cichlids
  • Shrimp

Schooling fish

  • Small Tetras
  • Rasbora
  • Corydoras Catfish

Aggressive fish

  • Betta

Big fish

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

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

Question #3 What Are Some Good 20 Gallon stocking ideas

Alright, here it is, the biggest stocking list for a 20 gallon tank that I could create.

There are 40 fish you can pick from.



Photo Credit: Cliff


Rasbora schooling fish for 20 gallon tank

Photo Credit: Drew Tyre

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


Platy gallon community tank

Photo Credit: Allie_Caulfield

  • Parrot Platy
  • Red Platy
  • Coral Platy
  • Red Diamond Platy


Fancy Guppy

Photo Credit: Jorge Correa

  • Endler Guppies
  • Fancy Guppies


German Blue Ram



Dwarf GouramiPhoto Credit: Bernat Arlandis

Corydoras Catfish:

Cory Catfish bottom dweller

Photo Credit: h080

  • Panda Corydoras Catfish
  • Albino Corydoras Catfish
  • Skunk Corydoras Catfish


Cherry Shrimp

Photo Credit: Emilia Murray


Betta Aggressive fish

Photo Credit: JellyFishKiller

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 not only easier to maintain but will provide you with the opportunity 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?

In general, when stocking your 20 gallon tank, try to have one or two larger “Centerpiece” fish and fill in the rest with a school of smaller fish and a few bottom dwellers like shrimp or catfish.

It’s really up to you!

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

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

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

Some great beginner plants are;

  • Java Fern
  • Java Moss
  • Anubias

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 a great size 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 full-grown, then it only has 18″ to swim back and forth and will only 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, not a lot of 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 out of all the fish I listed above, the Goldfish was not one of them. That’s because the smallest tank size that you should keep a goldfish in 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, Goldfish.

Other methods to determine stocking levels include;

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

In general, 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 what their specific needs are, 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 useful when looking at stocking some smaller-sized tanks.

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