Cardinal Tetra Tank Size: Minimum Size| Choose The Right One

Cardinal tetra is a small freshwater fish from the Characidae family. It has been famous as an aquarium species since American ichthyologist Leonard Peter Schultz referred to the cardinal tetra in 1956 as Cheirodon axelrodi. After that, these fish continues to be widely traded for hobbyist purposes nowadays. As this fish is widespread today, we will discuss the minimum size of the tank for Cardinal tetra.

The minimum tank size for Cardinal tetra is 20 gallons with a temperature of 24-28°C or 75 to 82 degrees Fahrenheit. Even though these fish are smaller in size, they are active and need enough room to swim. So you have to make sure that the tank size is 20 gallons, but larger tanks are always better since these fish grow up quickly and need more space in the future.

If your tank is smaller than this requirement, it will be hard for them to swim around the whole aquarium. In addition, it results in frequent bumping. Your fish will also feel tired quickly because of low oxygen concentration.

In this post, we will dig into the tank size, tank requirement, and ways to keep Cardinal tetra healthy. We hope this post will help resolve all your doubts about setting up a tank for these fish.

What Is The Minimum Tank Size For Cardinal Tetras?

When it comes to the minimum tank size for Cardinal Tetras, you need to know that there is no exact answer. This is because every single fish has different needs and requirements when it comes to its habitat.

However, most experts recommend a 30-gallon aquarium as your starting point if you are new to keeping these fish. This is because they are schooling fish that need at least six of their kind to prosper. Add more than one male into your tank, and you will have a breeding ground on your hands shortly after that.

Some people claim that an aquarium no smaller than 20 gallons would be their minimum tank size as far as other species are concerned. This is only if the species in question are fond of being in large numbers or require a lot of space to swim around and get active.

Moreover, some experts have been keeping Cardinal tetras in a tank of 20 gallons for years, and it is still thriving. Thus, this size is the absolute minimum for this species, but it is not the standard. It all comes down to your preferences and what you are willing to work with.

How Many Cardinal Tetras Can You Keep In Minimum Tank Size Of 20-Gallon?

This is the question that most of us ask when they buy them for the first time. You can keep 10-12 Cardinal tetras in a minimum 20-gallon tank size, which provides enough space for these fish. It comes out as a better option than keeping a few numbers of fish crowded in small tanks.

Usually, it is best to keep a group of at least six cardinal tetras in a tank. These are peaceful fish that won’t disturb the other inhabitants, but they need company all the time for their well-being.

What Will Happen If You Overcrowd Your Cardinal Tetras’ Tank?

Cardinal tetras grow to an average length of three inches, making the minimum tank size for one fish half a gallon.

If you have more than just one cardinal tetra in your aquarium, overcrowding will become inevitable, leading to several problems that are not good for these fishes’ health. For instance:

Cardinal Tetras Might Feel Stressed

Cardinal tetras are schooling fish. So they need to have other cardinal fishes near them at all times. They will not feel comfortable if there is no one else around. These fish are active, and they love to move ar0und.

If there is no room for them to move, they will not be as active as before. As a result, Cardinal tetras will feel stressed out.

Cardinal Tetras Might Be Prone To Illnesses

Overcrowding your fish in a small tank with little water volume and low oxygen levels invites various diseases. This might affect your cardinal tetra’s health. Bacterial and parasitic infections might occur if their immune system is down because of the lack of space and poor water quality. They can also contract fin rot, ich, and other diseases that can be fatal for cardinal tetras

Lack Of Oxygen

Overcrowding can lead to the lack of oxygen in your aquarium. If there is not enough room for all fishes, they might end up staying on the surface because it’s closer to where more oxygen is present. This will make them feel uncomfortable and stressed out even further.

Cardinal Tetras Might Fight With Each Other

When there are too many cardinal tetras in a small tank, and some of the fish get bigger than the others, these fishes will fight to establish their territory.

When Cardinal tetras are uncomfortable with each other, they might show their aggressiveness by flaring at each other. Theif fins might nip and tear up if the fight is too violent, leading to injuries that are very hard to heal.

Deterioration In Water Quality

When there are too many fish in a small volume of water, it can cause the deterioration of water quality, which will make your life difficult because you have to change the water more often. This is a hassle and might be more challenging for some people who cannot do that on their own easily.

What Are The Things To Consider While Choosing The Right Cardinal Tetra Minimum Tank Size?

Cardinal tetras are smaller in size, but they are very active fish. So it would be best if you had at least a 20-gallon tank for them. The other requirements of cardinal tetras are just like the rest of the characins are:

Water Quality

Cardinal tetras are very sensitive to water conditions. So it would be best if you had a well-established tank filled with high-quality water. In addition, your tank needs a proper filtration system to remove ammonia and nitrites. You can also use a well-established biological filter to maintain the water quality in your aquarium.

Remember to change the water frequently to keep your tank clean.

Aquarium Plant

Cardinal tetras are schooling fish, so they need a place to hide and sleep at night or when you turn off the light. You can use plants in your aquarium for this purpose. You also have other options like caves, wood, and rocks. All of these things will be helpful to make your aquatic environment natural and suitable for them.

Water Temperature

The ideal temperature for cardinal tetras is 75-81 degrees Fahrenheit or 24-27 degrees Celsius. But if your house climate does not fall in this range, don’t worry. The fish will feel fine as long as it is stable.


The pH level of the water should be between 4.6 and 6.2, or up to one point higher than neutral (pH seven). The ideal range is about three to four for breeding purposes.

Carbonate Hardness

Cardinal tetras are very sensitive to carbonate hardness levels in the water. So you need tank water with moderate carbonate hardness.

The Lighting Requirements

Cardinal tetras are very sensitive to water parameters, and lighting is another thing you need to consider while choosing the right tank size. The fish will feel comfortable in either low or high light conditions. But it would be best if you never kept them under bright lights for long periods.


In conclusion, if you want to keep these fish, it is important to know what tank size they require. The minimum recommended tank for cardinal tetras should be at least 20 gallons or more prominent, with plenty of plants and wood inside the aquarium.

If you are new to fish keeping, it would be better to buy a tank of at least 30 gallons. This is because your fish will grow more prominent over time, so you should have enough room for them to swim around in the tank.

Be attentive and enjoy yourself with your fish. Best of luck with your new fish tank!

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