How Many Neon Tetras Can You Keep in 20 Gallons?

A 20-gallon tank is an ideal sized home for between 10 and 15 Neon Tetras. Neon Tetras can grow up to 2 inches in length. The general rule of thumb for fish under 3″ is that you can keep 1″ of fish per gallon of water.

Let’s discuss how many tetras you can keep with some examples.

Neon Tetras | Source: Deposit Photos

How Many Neon Tetras Can Live Together in a 20-Gallon Tank?

Around 15-20 Neon Tetras can live together happily in a 20-gallon tank. 20 Neon tetras would give you room to add a few more fish, but not many. 15 would give you a little more room to add extra fish into the aquarium.

Neon Tetras are schooling fish and should be kept with at least 6 others of their own kind. (e.g. at least 6 neons, even if you have other types of tetra)

They are active, energetic fish and like to swim around, and so require enough space to do so freely without feeling crowded. This means that a 20 gallon long aquarium is a better choice to house them than a regular 20 gallon high aquarium.

This also gives enough room to fill the tank with plant life and décor. Neon Tetras like to swim through plants, rocks, and wood. This helps them feel safe and gives them somewhere to hide if they feel the need to do so.

How Many Neon Tetras Can You Keep in a 20-Gallon Tank with Other Fish?

If you’re going to stock other fish, you should generally only keep 10-15 neon tetras in your aquarium. This gives you enough other room to add some other fish into your aquarium as well.

Here are a few examples of what you could do in a 20 gallon long:

  • 15 Neon Tetras, 8 Corydoras
  • 20 Neon Tetras, 6 Pygmy Corydoras
  • 10 Neon Tetras, 10 Harlequin Rasbora
  • 10 Neon Tetras, 6 Zebra Danios, 1 Clown Pleco

It’s hard to say exactly how many fish you can keep in an aquarium without knowing exactly what types of fish you’re going to keep as well as whether or not you’re going to put a lot of live plants into your aquarium.

What type of filter you you also plays into this.

There are a few tools, however, that can help you estimate.

As I mentioned earlier, the general rule of thumb is one inch of fish per gallon of water. This isn’t an exact science (hence why you can keep 20 1.4″ long neon tetras in a 20 gallon aquarium), but it gives you a general idea for fish that are under 3″ long. (And the smaller the fish the better it works.)

You can also check out Aqadvisor and play around with your aquarium setup.

The best choice would be to join a forum like fishlore and ask for advise about specific fish you are thinking of adding to your aquarium. They will be able to tell you specifically which fish will work together and what’s best to avoid.

Which Fish Can You Keep as Tankmates with Neon Tetras in a 20-Gallon Tank?

Neon Tetras are peaceful, not aggressive fish, and get along well with other small, peaceful fish in a community tank.

Good tankmates for Neon Tetras include:

  • Guppies
  • A Betta (Depending on the betta’s personality)
  • Zebra Danios
  • Apple Snails
  • Ghost Shrimp
  • Kuhli Loaches
  • Honey Gourami
  • Corydoras
  • Harlequin Rasboras
  • Neon Rasboras
  • Cherry Barbs
  • Endler’s Livebearers
  • White Cloud Minnows
  • Platies
  • Mollies
  • Small Plecos

Generally speaking, you may still want to avoid adding other tetras into your aquarium, because even if they get along well, the more tetras you add the more likely you are to have a run-in with neon tetra disease, which can wipe out an entire tetra population and can even spread to some non-tetra fish.

If you’re willing to take the risk, small tetras that have a peaceful disposition (such as cardinal or ember tetras) can be a good option for keeping in your aquarium when you have neons.

Which Fish Should You Not Keep in a Tank with Neon Tetras?

Fish that are large and aggressive should not be kept with Neon Tetras, as they can see the Neon Tetras as prey. They could bully the Neon Tetras, or if their mouth is wide enough, they can swallow the smaller fish. Any fish that require different water conditions should not be kept with Neon Tetras.

Bad tankmates for Neon Tetras include:

  • Angelfish
  • Large Gourami’s (such as Pearl or Opaline)
  • Large Cichlids
  • Large Tetras (such as Panda or Congo)

How Do You Introduce Neon Tetras into a 20-Gallon Tank?

You should introduce Neon Tetras into a tank gradually so that they can acclimatize to the water conditions, and so that the tank filtration system has time to adjust to the added bioload. If you are adding 10-15 Neon Tetras into a 20-gallon tank, add 6-8 at a time – add 7 one week and the remaining 7 the week after.

Bioload is the waste produced by fish, which changes the conditions of the water. More fish create more waste, meaning the tank should be cleaned and water replaced more regularly. Adding a filtration system and air pump into the tank helps keep it clean.

Also, you want to make sure you’re getting your neon tetras from a trusted source. Do not just buy tetras from the local pet store and throw them in your aquarium. You may regret it.

If possible, get your neon tetras from a local hobbiest or breeder with a good track record for tetras that don’t have neon tetra disease.


You can keep 15-20 neon tetras in a 20 gallon aquarium. You should keep no fewer than 6. If you want to keep other fish in the aquarium with your tetras, it may be better to keep 10-15 tetras to leave room for your other fish.

How many tetras you can keep with other fish depends on the size of the fish and how many of them you want to keep. A lot of other fish need to be kept in groups of at least 6, so that’s something you want to keep in mind when planning how you want to stock your tank.