How Many Cardinal Tetra In A 10-Gallon Tank?

How Many Cardinal Tetra In A 10 Gallon Tank

Cardinal tetras are one of the most beautiful freshwater fish you can ever find. Moreover, they are one of the best community fish you can find. So, if you plan to keep Cardinal Tetra, you should at least pick a 10-Gallon Tank.

Now the question arises, how many Cardinal Tetra to keep in a 10-Gallon Tank?

The simple answer is 8. Yes, you read that right.

So, let’s find out…

Cardinal Tetra is 1.25 inches long. Therefore, we have a golden ratio to find the water volume required below 3 inches long, i.e., one gallon per inch. So, calculating, 10/1.25=8.

We can keep 8 Cardinal Tetras in a 10-Gallon Tank.

What Tank Size Does Cardinal Tetra Need?

Cardinal Tetras are schooling fish that needs enough empty space to swim around. So, to start with a species tank, a tank of 20-Gallons is the right size for 16 Cardinal Tetras.

However, if you are looking for a community tank, you will at least need to start with a 30-Gallon tank for Cardinal Tetras and its tank mates to live a comfortable and healthy life.

Minimum Tank Size For Cardinal Tetras?

As I have mentioned earlier. Cardinal Tetras need enough swimming space and needs to be in a group. A small group of 6-8 Cardinal Tetra fish needs a minimum of 10-Gallon fish tanks.

How Many Cardinal Tetras Per Gallon?

One challenge for fishkeepers is knowing how many Cardinal Tetras they can keep in a tank. Unfortunately, there are no definitive answers to this question as it depends on the size of the individual tetra; a small tetra counts as one tetra while a large or average-sized one counts as three.

When it comes to calculating how many Cardinal Tetra can fit in a tank, you should use a higher estimate for individual fish size.

Cardinal Tetra grows up to 1.25 inches long.

A general rule is to calculate the water volume that fish smaller than 3 inches require to survive. One inch of fish requires one gallon of water.

Again, an adult Cardinal Tetra is 1.25 inches long, so one adult Cardinal Tetra needs 1.25 gallons of water.

Likewise, a 10-Gallon tank allows you to keep 10/1.25=8 Cardinal Tetra fish.

How Many Cardinal Tetras Should Be Kept Together?

Cardinal Tetras are schooling fish; they need to stay in a group. Therefore, Cardinal tetra should be kept in groups of at least 6.

As they are moderately peaceful and non-aggressive fish that do not nip any fins or harm their tank mates, you can keep a group of Cardinal Tetras in a community tank.

Is It Possible To Add More Cardinal Tetra To A 10-Gallon Tank?

Yes, it is possible to add more than 8 Cardinal in a 10-gallon tank if you maintain your aquarium.

However, I don’t recommend you to add more than the recommended number. This is because Cardinal Tetras are very active swimmers. So, they need enough open space to swim around.

If you still want to add more Cardinal Tetras to your tank, you can go for 10 Cardinal Tetra in a 10-Gallon tank with well-maintained aquarium water conditions.

Are Cardinal Tetras Hard To Keep In?

No, Cardinal Tetras are some of the easiest fish to care for.

Cardinal Tetra is a hardy fish that can adapt to most of the water conditions. However, it is important to maintain the tank and keep the aquarium clean so as to avoid any sort of disease or infection in your Cardinal Tetras.

Hence, keeping Cardinal Tetras are not difficult if you bear these things in mind.

Aquarium Requirement For Cardinal Tetra Fish In 10-Gallon Tank

Aquarium condition is essential for the tank to thrive. It may seem like a 10-Gallon tank would be much simpler to maintain than a larger tank because of its size, but it still requires just as much care.

Maintaining a healthy aquarium can be difficult and complicated. But it’s not impossible with what I am about to guide you with.

The most important factor that you should consider when keeping any kind of fish is their environmental condition. You cannot be careless regarding this as the health of your fish depends on it. Hence, you should be thorough regarding tank maintenance.


Some filters, like power and hang-on back (HOB) filters work better for small tanks. However, you should make sure that your HOB is large enough to contain biological media without any issues with water circulation.

I have been using AquaClear, Fish Tank Filter For 5 to 20 Gallons on all my 10-Gallon Tanks.

Water Temperature

Temperature is one of the most important factors to be considered in fishkeeping. The temperature should always fall between 76-82°F. This is because Cardinal Tetras prefer temperatures around 77°F – 80 ° F, and have a lower tolerance for higher temperatures. You should provide your tetra with cooler water if you live in an area where the water is usually warmer than 82°F.

If you use a filter, the temperature of your tank’s water can be regulated by the amount of flow coming out from it. A higher flow rate will cause more heat to be taken away effectively by leaving the tank cooler and vice versa.

This is why choosing an aquarium heater is also important. You should only use heaters that are specifically designed for aquariums. Submersible ones work better because they are adjustable, and you can change the temperature of the water by turning a knob.

I recommend you to buy Fluval 5 Gallon Aquarium Heaters as they have been specially made with consideration to avoid any issues regarding overheating of water in tanks of small size such as 10-Gallons.

Water Hardness

Cardinal Tetras need a water hardness that falls between 4 dH to 7 dH.

You should perform water changes at least once every two weeks while following the above-mentioned parameters. If your aquarium’s water isn’t just right, you should go for an RO/DI unit to remove excess salts from the water.

Moreover, you can maintain water hardness by adding crushed coral into your tank, but keep in mind not to add too much of it at once as it may cause an increase in pH levels that will be harmful for your fish.

Water pH

Cardinal Tetra prefers a water pH that falls between 4.0 and 8.0 with a tolerance of 6.5 and 8.5.

Keeping the water’s pH around 7 to 8 will be possible by performing frequent partial water changes every week or two weeks depending on how much you are able to do it, and using an air pump if the water gets too acidic.

Cardinal Tetras are very sensitive to high levels of ammonia, so I recommend that you perform a larger number of water changes in order to keep your aquarium safe even for the long term.


Cardinal Tetras are usually kept in a community tank, so there is no need to have separate decorations for them. However, this does not mean that they will be fine with any decoration you choose.

For example, plants are a must when it comes to aquariums because fishes need places where they can hide and ambush their prey. Moreover, plants will not only offer shade, but they will also maintain water parameters by consuming harmful elements such as nitrates.


Cardinal Tetras look better when they are kept in an aquarium containing live plants. Some great choices for your Cardinal Tetra tank would be Amazon Sword, Anubias Nana, Water Wisteria, and Java Fern.

Cardinal Tetras prefer darker places so it is best to use floating plants with a lot of shade if you want them to get along with each other.


Cardinal Tetra do not necessarily need a light for your tank, but it will surely help you to see more of their natural behavior.

If you want to keep your Cardinal Tetras happy and healthy, I recommend buying the AQUANEAT LED Aquarium LightThis one is specially designed with consideration to use in tanks of small size.

It outputs the right amount of light that you need for your Cardinal Tetras and it comes with a built-in timer and dimmer as well. This makes setting it up very easily, so you will not have to worry about doing anything else while you are at work or asleep.


Cardinal Tetra is usually kept on a substrate of sand, but it can adapt to gravel and soil as well. However, it is important that you remove any sharp objects such as rocks and ceramic pieces from the tank.  These might injure your Cardinal Tetras’ tails when they swim around or hide inside the plants.

You will need to vacuum the gravel/sand once every week or two weeks, depending on how much waste your Cardinals have produced.

How To Maintain Aquarium Condition On A 10-Gallon Tank?

Aquarium condition is essential for the tank to thrive. Maintaining a healthy aquarium can be difficult and complicated, but it’s not impossible with these simple steps. It may seem like a 10-Gallon tank would be much simpler to maintain than a larger tank because of its size. But it still requires just as much care.

Cardinal Tetra are some of the most sensitive fishes when it comes to water changes. Hence, they require frequent small changes rather than a few larger ones.

If you want your Cardinal Tetras to live more, make sure you perform water change in every week or two weeks. You should also perform partial changes while you are doing water changes to keep the waste levels stable.

You can perform partial water changes by siphoning out about 10 % of the total water; and replacing it with fresh and clean water.

Since Cardinal Tetra likes living in peaceful environments; never change more than 30 % of their tank’s water at once since it will cause a lot of stress for them.

You should also replace the water when the nitrate and ammonia levels exceed 0.25 ppm. It is best to pay extra attention to your Cardinal Tetras if you keep other fish in the same tank. Because ammonia may reach toxic levels if you don’t care about them properly as well.


I hope that you have good knowledge about the necessary requirements when it comes to caring for Cardinal Tetras in a 10-gallon tank. In particular to take note of are proper care, timely feeding, and providing them with a secure environment.

I’m sure if you can provide all this for your fish they will thrive well.

If you want to know more about other Tetra fish, you can check out our other articles as well.

Scroll to Top