How Many Tetra Fish Per Gallon of Water?

tetras per gallon of water

Tetras are one of the popular home aquarium fish. The tetra fish are inhabitants of different regions such as Central America, South America, and Africa. These fish are one of the hardiest fish that you can keep in your tank. The experts, as well as beginner fish keepers, prefer the tetras. However, one of the commonly arising questions is how many tetra fish can you keep per gallon. This is also one of the tricky situations when building an aquarium environment. This article will be all about the quantity of tetra fish that you can keep per gallon of water in your tank.

The answer to how many tetra fish per 2-Gallon of water is 1 tetra fish. Since tetra fish have a slim body, we take the golden rule:1 gallon of water per inch of fish. So, using the formula: total tetra fish on an aquarium is equal to a total gallon of the aquarium divided by average size(inch) of your tetra fish species, we get a 2-Gallon/2 inch of fish, that is 1 Tetra Fish.

Total Tetra Fish On My Aquarium = Total Volume of My Aquarium (in a gallon) / Average Size of My Tetra Fish (in inch)

Other factors like tetra nature, tank total volume, tankmates, etc. also need to be taken into account. Hence, keeping all these factors in mind, I want to give you a good concept about how you can help your tetras to flourish in the tank by keeping them in just the right quantity.

Continue reading further to learn more.

About Tetra Fish

Tetras are tropical, freshwater fish. And these fish are also one of the hardiest fish that can adapt to different water parameters if there are subtle changes in their environment.

One of the striking factors about tetras, which attracts most people, is their bright and beautiful colors across their bodies.

Apart from this, tetras are also known for their friendly and social behavior. They are compatible with many other species and does not have any violent nature.

Furthermore, tetras are not supposed to live alone as these tetras are schooling fish. They will mostly be happy and stress-free when they are in groups.

Tetra owners are aware that they need at least 5 to 6 tetras together in a tank. This brings the question, exactly how many of the tetra fish can you keep per gallon of water.

Now, the question is about the number of tetras suitable for your tank. You can have a tank size of 5, 10, 20-gallons, or even more.

The ideal tank size for tetra fish starts from 10-gallons but you can also keep small numbers in a smaller tank.

If you want to know more about the tetra tank setup, check out our article on how to set up a tetra fish tank.

Rules for Calculating Quantity of Tetra Fish

You can follow various rules to determine the number of tetra fish you can keep in your tank.

First, you must be aware of your tank size. Half of your work is accomplished when you know about tank size, shape, area coverage, etc.

Here are some of the formulae you can follow to calculate the number of tetra fish you can keep in your tank per gallon of water.

General Rule of Thumb

This is the most popular rule many tetra fish owners follow to determine the number of tetra fish to keep in the tank. This rule is quite simple as well.

The rule states, for every one inch of fish, you need one gallon of water. You can use this rule in the case of tetra fish.

As most of the tetras are comparatively smaller than other species, the general rule of thumb is the ideal rule for them.

This rule can be difficult to manage if you have tetras that are larger than 3 inches. The size of most tetras falls under this so you will not have much problem. Additionally, you need to follow this rule only with tetras that have grown fully.

Let us consider a 10-gallon tank. Tetras such as neon tetras grow about 1.5 to 2 inches in length.

Now, also keeping in mind the different decorations in the tank, let us consider we have around 8-gallon in total. From this, we can calculate, 8-gallons / 2 inches of fish length = 4 tetra fish.

Thus, you can keep around 4 neon or cardinal tetras if you have a 10-gallon tank.

Surface Area Rule

This is the mathematical version to calculate the number of tetra fish in a tank. In the case of slimmer and smaller fish like tetras, you will be able to follow this rule very easily.

According to this rule, every inch of fish requires 1 square foot of surface area. This will not the same case if you have wide-bodied fish.

To implement this rule, you will need to know the surface area of your tank. After that, you will calculate the quantity of fish just as you calculate using the general rule of thumb.

Considering Tank Mates

As I have mentioned in the previous section of the article, tetras are schooling fish and are compatible with many other fish species. Due to this, you also need to keep in mind the possible tank mates for your tetra fish.

Hence, you need to have enough space for other tank mates for the tetras. Tetra fish prefer companions that are active and energetic like themselves. Tetras do not do very well with aggressive and large species.

Consequently, you will have to be careful when choosing tank mates. Mostly you need to focus on the space that tetra tank mates can consume. Make sure that your tank is never overcrowded.

Overcrowding can lead to an increase in pollutants and toxins in the tank, which will not be ideal for species living in the tank.

Tetra Fish Tank Mates Combinations for Different Gallons

With different sizes tanks, you can have a school of tetras along with other fish in the same tank. In this part of the article, I will mention different tank mates for tetras that you can keep in tank sizes ranging from 5-gallons, 10-gallons, and 20-gallons.

Also Read: How Many Tetra Fish Per Gallon of Water?

5-Gallon Tank

If you are choosing to keep a 5-gallon tank (Buy Online) for tetras, I will not recommend it.

Note: 5-gallon tank can be equivalent to 19 liters.

This is because tetra fish are very active swimmers and want free space to explore. These fish also need a good hiding spot to use whenever they feel stressed.

Hence, you will have only limited species to choose from in a 5-gallon tank. Despite this, you can keep neon tetras in this tank.

You will be able to house 5 to 6 neon tetras with only 1 other species. The tank mates for tetras in a 5-gallon tank can be snails.

10-Gallon Tank

For a 10-gallon tank (Buy Online), you will have a wider variety of tetra fish species that you can choose from.

Even though a 10-gallon tank is still small to house many species, you may be able to mix up other species with your tetras.

You can keep 6 tetras in a school with other 2 smaller schools of different fish. Some options that you can have are neon tetras, ember tetras, cardinal tetras, lemon tetras, etc. Moreover, the tank mates for these tetras can be guppies, ghost shrimps, or snails.

Related Article: How Many Neon Tetras in a 10-gallon tank

20-Gallon Tank

The general concept of aquarium keeping is that the bigger the tank, the better. Not just that you will be able to keep much fish in the tank, it will also be a lot easier to maintain the tank as well.

For a 20-gallon tank (Buy Online), you will be able to keep different schools of tetras such as neon tetras, lemon tetras, red eye tetras, cardinal tetras. In a school, you can keep up to 6 to 8 tetras.

The tank mates for this kind of aquarium can be danios, snails, panda cories, ghost shrimps, guppies as well as platys.


When you are keeping tetras, you also should ensure that your tetras do not harass other species as well. If tetras are in an overcrowded space, you can see them stressed and not as active as they supposed to be. On the other hand, if you isolate them they will start to nip their fins.

I hope that from this article, you have some perspective on how to calculate the quantity of tetra fish that you can keep per gallon of water in your tank.

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