How Many Neon Tetras In A 20 Gallon Tank? (rule Included)

The proper stocking of a neon tetra can be compared to a work of art. Seeing the color explosion of blue and red and the geometric patterns present on the tank is simply a fantastic sight to behold. 

A 20-gallon aquarium for neon tetras would be a good starting point for those new to the hobby. It then comes to the question: how many neon tetras in a 20 gallon tank? 

In this article, we will find out the answer to that question. 

How Many Neon Tetras In A 20 Gallon Tank? 

The number of neon tetras that you can add to a 20-gallon tank will range from 10 to 30. You may be scratching your head at that number, but I will explain. It’s a good idea to start with the number of 10. However, if you are an experienced fish keeper who is confident enough with overstocking to do it safely, 30 fish is perfectly manageable. 

From what I have found, there have been hobbyists who have successfully kept and recommend keeping 30 neon tetras in a 20-gallon tank. 

You can keep from 10 to 30 neon tetras in a 20-gallon tank
You can keep from 10 to 30 neon tetras in a 20-gallon tank

Nevertheless, it is also important to note that the stocking number also depends on what kind of tank you have. If you have a 20-gallon long tank, you can definitely raise more neons than what a 20-gallon high tank would allow due to its bigger footprint. 

Having a 20-gallon long tank will allow you to raise more neons than you would in a similarly-sized tank but high because of its bigger footprint.

To decide the stocking number, hobbyists follow many rules to ensure that this number is accurate. The most widely used rule is “1 inch per gallon”. 

Let me show you what would happen if the stocking numbers followed this rule. 

The 1 Inch Per Gallon Rule 

There is some debate over this rule. It is because it doesn’t take into account the space occupied by decorations, plants, and substrates. It also completely ignores the fish’s height during the calculation. 

Although, according to the general notion, this rule may be able to be applied to fish that are smaller than 3 inches. For larger fish, you should not use this rule. For example, it is not recommended to add a 12-inch oscar to a 12-gallon tank. 

The average length of neon tetras is about 1.5 inches (4 cm). I’ll assume they’re 1.75 inches (4.45 cm) long for the purposes of this calculation. 

As a result, a 20-gallon tank would house 11.42 neon tetras (20/1.75). If rounded up, you would get 11 or 12. 

The answer, however, heavily depends on factors such as how frequently you are willing to do water changes, the number of decors and plants you have in your tank, and your experience in keeping fish. 

What Happens If I Overcrowd My 20-Gallon Neon Tetra Tank?

Let me ask you this question. How would you feel if you were trapped in a small room with 40 other people and where there was no way out?

It is hard to imagine that anyone can survive in a confined area where there are no places to move.

A similar thing happens to neon tetras when they are confined to a 20-gallon tank with too many neon tetras or others. You should never push beyond the limit, as it will only turn into a nightmare.

It is very likely that the ammonia levels in the tank will be high because of the excretion of neon tetras. Consequently, it will be impossible for any of the beneficial bacteria in the tank to perform nitrogen cycling in the aquarium.

It will be impossible for these bacteria to convert all of the ammonia and nitrite into nitrate. Overload will also kill these helpful bacteria.

Neon tetras will die from aquarium Ammonia poisoning, pollution, and unclear, foamy water.

As a result, you will find some of your tetras will be stressed, gasping for air, or even trying to swim to find a place to rest or to breathe.

Stress has been proven to weaken the immunity system of neon tetras. Along with this, the peaking of pollution in the tank can bring in disease-causing agents.

In an aquarium with more fish than recommended, you are putting neon tetras at risk of death.

Video: Neon Tetra Tank Planted 20 Gallon


How many neon tetras should be together?

As a schooling species, neon tetras should keep a minimum of six to ten together in one tank. If you keep too few neon tetras together, they may become uncomfortable, stressed, and even die.

How long does it take for neon tetras to reach full size?

Neon tetras grow very fast. Neon tetras are small fish that grow to full size after about a year. The neon tetra usually grows up to about 1.4 inches (3.5 cm) in length, but some specimens have been known to grow to a maximum size of more than 2.3 inches (6 cm).

Do neon tetras need light?

In order for tetras to thrive, their tanks need to be illuminated with lights at least 12 to 14 hours a day, just like other tropical fish. In this way, they will be able to maintain a regular circadian rhythm. It is highly recommended to make your lights on a timer so that your fish can get used to a routine and establish a habit.


An aquarium of 20 gallons is the perfect size for a beginner. Neither is it big enough to overwhelm you with work nor is it small enough not to leave any room for mistakes.

It is possible to keep anywhere between 10 and 30 neon tetras in a 20-gallon aquarium. Beginners should stock 10-12 fish when getting their feet wet in the hobby. And once you gain enough confidence in your ability and knowledge, you can stock up to 30 fish at a time! 

However, the higher the number of fish, the greater the maintenance requirements. 

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