How Many Neon Tetras In A 20-Gallon Tank?

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The first question I had when I first got my 20-gallon tank was how many neon tetras I can have with this aquarium.

I always wished for a large group of neon teras, mainly because of how beautiful they look when they are all swimming together. But I had no idea how many I should get.

In this article, I will answer this question, and also provide some tips on how to keep your neon tetras healthy within this tank size.

Let’s dive right in.

The Ideal Number Of Neon Tetras For A 20-Gallon Tank

For a 20-gallon tank, you can comfortably keep around 10 to 12 neon tetras.

This quantity takes into account their need to live in groups and allows for enough space to avoid overcrowding, which ensures a healthier environment for the fish.

How To Calculate The Number Of Neon Tetras You Can Keep In A 20-Gallon Tank

This is how you roughly calculate the number of neon tetras that can be kept in 20 gallons:

  • Start with the general rule of thumb for stocking aquariums: 1 inch of fish per gallon of water.
  • Consider the average adult size of a neon tetra, which is about 1.5 inches.
  • Divide the tank’s capacity (in gallons) by the size of the fish (in inches). In this case, 20 gallons divided by 1.5 inches equals approximately 13.3.
  • Round this number down to avoid overcrowding: approximately 13 neon tetras.
  • To ensure adequate swimming space and accommodate other tank objects, it is advisable to reduce the rough calculation by a reasonable percentage.
  • That is why 10 to 12 neon tetras in a 20-gallon tank is the best option, accounting for decorations, plants, equipment, and other fish.

Why Is A 20-Gallon Tank Considered The Ideal Size For Neon Tetras?

It is widely accepted that a 20-gallon tank is the ideal choice for neon tetras, and for a couple of reasons:

  • Sufficient Space: Neon tetras need adequate space to swim and school together. A 20-gallon tank provides this without overcrowding.
  • Stable Environment: Larger tanks like 20-gallon ones tend to maintain more stable water conditions, such as temperature and pH, which are essential for neon tetras’ health.
  • Group Living: Neon tetras are schooling fish, which means they like to live in groups. A 20-gallon tank allows for a good-sized group of tetras while ensuring each fish has enough space.
  • Reduced Stress: Adequate space and stable conditions reduce stress for the fish, leading to healthier, more vibrant tetras.
  • Decorative Scope: A 20-gallon tank provides sufficient room for the addition of plants and other aquarium decorations, which can mimic the tetras’ natural environment and enhance their well-being.
  • Compatibility with Other Species: The tank size can also accommodate a few other compatible species, allowing for a diverse, community aquarium.
  • Easier Maintenance: Larger tanks like a 20-gallon tank require less frequent cleaning compared to smaller ones due to the dilution effect, making maintenance a bit easier for the owner.

Also Read: Neon Tetra Tank Size

Tips For Successfully Raising Neon Tetras In A 20-Gallon Tank

Growing neon tetras in a 20-gallon tank can be pretty straightforward, but I still recommend following these steps:

  • Monitor Water Conditions: Maintain a water temperature of around 70-81°F (21-27°C) and a pH level between 6.0 and 7.0, as these are ideal conditions for neon tetras.
  • Regular Cleaning: While a 20-gallon tank dilutes waste more than smaller tanks, it’s still important to perform regular water changes (around 10-15% weekly) to prevent the build-up of harmful chemicals.
  • Provide Proper Diet: Feed your neon tetras a diet of high-quality flake food, brine shrimp, and daphnia. Feed them small amounts twice a day, amounting to what they can consume in 3 minutes or less each feeding.
  • Keep an Adequate School: As schooling fish, neon tetras thrive in groups of 10 or more. In a 20-gallon tank, a group of this size is manageable and provides enough space for all fish.
  • Use Tank Decorations: Include a variety of plants and hiding spots to mimic their natural environment and provide them with a sense of security.
  • Set Up Lighting: Neon tetras originate from shaded environments, so use subdued lighting or provide plenty of plant cover to replicate this.
  • Acclimate Slowly: When introducing tetras to the tank, allow them to acclimate to the water temperature by floating the bag they came in for about 15 minutes.

Also Read: How Many Neon Tetras In A 10-Gallon Tank?

Does The Gender Of The Neon Tetras Matter?

No, the gender of neon tetras does not matter when housing them in a 20-gallon tank.

Both male and female tetras can coexist peacefully and engage in similar behaviors, making the tank equally suitable for tetras of either gender.

Will A 20-Gallon Tank Become Overcrowded Due To Breeding? 

Yes, a 20-gallon tank can potentially become overcrowded if neon tetras breed and produce offspring.

However, it’s important to note that breeding neon tetras in a home aquarium setting can be challenging due to their specific water condition requirements and the fact that adult tetras may eat their own eggs or fry if not separated.

Is Breeding Neon Tetras Feasible In A 20-Gallon Setup?

Yes, breeding neon tetras in a 20-gallon setup is feasible, although it can be a bit challenging. Here are some tips:

  • Create a Breeding Environment: Lower the water level to around 6 inches and darken the tank, mimicking the rainy season in their natural habitat which triggers spawning.
  • Maintain Water Conditions: Keep the water soft and acidic (pH around 5-6) as these are ideal conditions for spawning.
  • Feed a Nutrient-Rich Diet: Prior to breeding, feed the neon tetras a diet rich in live foods to prepare them.
  • Separate Adults After Spawning: After the eggs are laid, remove the adult tetras from the tank to protect the eggs and emerging fry from being eaten.

How Often Do Neon Tetras Breed?

Neon tetras do not adhere to a strict breeding schedule, and their ability to breed in a 20-gallon tank largely depends on achieving optimal conditions, which can be quite demanding.

For successful breeding, it is crucial to recreate their natural environment, including soft and acidic water, as well as lower light levels.

Additionally, providing them with a nourishing diet plays a significant role. Under these ideal circumstances, neon tetras may breed approximately every couple of weeks.

Also Read: How Many Neon Tetras In A 30-Gallon Tank?

Can You Add More Neon Tetras To A 20-Gallon Tank?

Adding more neon tetras to a 20-gallon tank needs to be done carefully to ensure a healthy environment for all fish. Keep this in mind:

  • Current Population: Consider the current number of fish in your tank. As a general rule, aim for about 1 inch of fish per gallon of water, remembering that neon tetras can grow up to 2 inches long.
  • Gradual Introduction: To avoid a sudden load on the tank’s bioload, introduce new neon tetras gradually, not more than 2-3 at a time.
  • Quarantine New Fish: To prevent the spread of disease, it’s crucial to quarantine new neon tetras for at least two weeks before introducing them to your main tank.
  • Acclimation: Ensure you acclimate the new tetras to the water conditions in your tank before releasing them. This process usually involves floating the bag they come in within the tank for about 15-30 minutes.
  • Monitor Behavior: After adding new fish, keep a close eye on the tank’s inhabitants. If you see signs of stress or aggressive behavior, it may be a sign that the tank is becoming overcrowded.

What Is The Optimal Number Of Neon Tetras To Keep Together

The ideal number of neon tetras that should be kept together is six, as they are schooling fish and need companionship to reduce stress.

However, in a 20-gallon tank, you have the ability to keep a larger group of 10-12 neon tetras together, which is even better.

This allows for more natural schooling behavior, resulting in healthier and happier fish.

Keeping Neon Tetras With Other Fish In A 20-Gallon Tank

Naturally, you’ll want to add other types of fish to your neon tetras tank. Fortunately, 20 gallons offers a decent amount of options.

Here is a table summarizing the ideal numbers with some common species:

Fish CombinationQuantity (in 20 gallons)
Only Neon Tetras10-12
Neon Tetras and Guppies10-12 Tetras, 6-8 Guppies
Neon Tetras and Mollies10-12 Tetras, 4-6 Mollies
Neon Tetras and Zebra Danios10-12 Tetras, 6-8 Danios
Neon Tetras and Platy Fish10-12 Tetras, 5-7 Platies
Neon Tetras and Betta Fish10-12 Tetras, 1 Betta

1. Neon Tetras And Guppies

In a 20-gallon tank, you can typically house around 10-12 neon tetras alongside 6-8 guppies. 

Both species are small, peaceful, and prefer similar water parameters, making them good tank mates. However, make sure to monitor the tank to prevent overcrowding.

2. Neon Tetras And Mollies

Given mollies’ slightly larger size, a balanced 20-gallon tank setup could include about 10-12 neon tetras and 4-6 mollies.

These species are generally compatible but remember that mollies require a bit more space to swim comfortably.

3. Neon Tetras And Zebra Danios

A 20-gallon tank could comfortably accommodate around 10-12 neon tetras and 6-8 zebra danios.

Zebra danios are energetic swimmers and enjoy space to move around, so it’s essential not to overstock the tank and monitor the fish for any signs of stress or aggression.

4. Neon Tetras And Platy Fish

In a 20-gallon tank, you can consider housing 10-12 neon tetras along with 5-7 platy fish. 

Both species are peaceful and have similar water condition requirements, which makes them compatible tank mates.

However, given their active nature, it’s crucial to ensure that there’s enough space for everyone.

5. Neon Tetras And Betta Fish

You can keep one Betta fish with around 10-12 neon tetras in a 20-gallon tank.

Betta fish are solitary and can sometimes be territorial but given the size of the tank and the peaceful nature of neon tetras, they can usually coexist.

Always monitor for signs of aggression, especially from the Betta, to ensure all fish remain healthy and stress-free.


A 20-gallon tank can hold up to 13 neon tetras, although it is better to be on the safe side and get about 10 to 12.

You shouldn’t worry too much about breeding, though. Neon tetras don’t breed that easily, and they are not likely to overwhelm your tank.

You can also mix other types of fish along with your neon tetras, such as guppies, platy fish, and mollies. Just bear in mind that each has its own tank size requirements.