How Many Cardinal Tetras Can I Put In A 7 Gallon Tank?: Tips And Facts

There are many types of fish that can thrive longer in a tank. Some fish works better alone, while others need a group to move, swim, and eat in captivity. The cardinal tetra is an example of this second type of fish. Since it gets along with most other fish species, you can keep them in a small tank with just one or two other cardinal tetras. But do you know how many Cardinal tetras to put in a 7-gallon tank?

The number of Cardinal tetras in a 7-gallon tank depends on the size of the fish and the number of other fish living. In addition, you must get a good filter for your tank along with proper lighting. However, the cardinal tetra is not very demanding for their environment since they can live under most conditions.

In this post, we will talk about how many cardinal tetras you can put in a tank, what kind of filter is good for the tank, and about lighting. Hopefully, it will be worth giving your time to read this post.

How To Calculate The Number Of Cardinal Tetras To Put In A Tank?

The first thing you need to do is determine how large of a school you want. It’s generally best for the cardinals to be in groups of at least six, though if they are not swimming together, it will still work out fine.

A good rule-of-thumb is three females per male. So depending on your group size, you can work backward to figure out how many fish should be in your tank. Each cardinal tetra will want about two gallons of space. Thus, if you have a school of eight Cardinal tetras, it’s best to get an 18-gallon tank.

The next step is figuring out the pH level and temperature of the water that Cardinal tetras need in their tank. It is also important to remember that the cardinals will do best at a pH level of around six or higher. If you want these fish to live longer and happier, you must keep them between seventy-two and eighty degrees.

How Many Cardinal Tetras Can I Put In A 7 Gallon Tank?

If you have a tank of 7 gallons, then it is better to keep only one or two cardinal tetras in it. However, if you want to save more, make sure that the tank is at least 14 gallons. The cardinal tetras will need at least two and a half feet in length just for their fins to stretch out. The water temperature should be between 72 and 80 degrees Fahrenheit, with the pH balance around six points five.

The substrate of your tank can either be gravel or sand. It is entirely up to you which one you choose. It would help if you also made sure that the decorations in your tank were not very sharp or pointy because this can hurt these fish. If you happen to be keeping live plants, then they will need at least three watts of light every hour just for them to survive.

You should regularly check your water quality since cardinal tetras do not have a natural defense against diseases. Therefore, if you notice that they are not acting normally, this could mean something wrong with the water.

What Species Of Cardinal Tetras Can You Put In A 7 Gallon Tank?

There are many cardinal tetras that you can put in a seven-gallon tank. But it is important to know which ones. Some cardinal tetras can get too big for a seven-gallon tank, while others are not compatible with the other species. The following is a list of some appropriate Cardinal tetra species to put in your aquarium:

Cardinal Tetra (Paracheirodon axelrodi)

This Cardinal tetra is one of the most popular fish in an aquarium. It can grow to be about three inches long. But it has a slim body that looks great when viewed from above or below.

Cardinal Tetra (Paracheirodon simulans)

The cardinal tetra is native to South America and prefers slightly acidic water with temperatures around 77 degrees Fahrenheit. This species is easy to care for and can grow up to about three inches long.

The Flame Tetra (Hyphessobrycon flammeus)

The flame tetra has a red stripe that runs its entire body length, including dorsal, anal, pectoral fins, and tail fin. It grows to about two inches long and prefers slightly acidic water with temperatures around 77 degrees Fahrenheit.

The Glowlight Tetra (Hemigrammus erythrozonus)

The glowlight tetra is another popular species of cardinal tetras because its red stripe looks stunning near-black background. It can grow to be about two inches long but usually stays smaller.

Black Cardinal tetra (Pristella maxillaris)

This species of cardinal tetra is the black neon. It has a dark gray body. It can grow to about two inches long but usually stays smaller.

What Are The Things To Consider When You Keep Cardinal Tetras In A 7 Gallon Tank?

Cardinal tetra is a prevalent fish in the aquarium industry. People love to have them because they are easy to care for, and they add color to an otherwise dull tank. They also get along well with their tank mates, making it even easier for you as a hobbyist.

However, there are few things to consider when you put Cardinal tetras in a seven-gallon tank. Such as:

Size Of Cardinal Tetras

Cardinal tetras can grow up to two inches in length. Since they stay small and do not outgrow themselves, you can keep them in a smaller tank. Don’t worry about the tank size until you fulfill their optimum tank parameters.

The Number Of Cardinal Tetras

When you put cardinal tetras in a seven-gallon fish tank, it is best to keep them as single species. This will ensure that they do not hurt each other and live happily together. You should avoid keeping more than six of these fishes in your aquarium because more significant numbers might stress the smaller ones out and lead to health issues.

Water Parameters For Cardinal Tetras

Cardinal tetras are very sensitive to water parameters. This means that you will have to be extra careful with the pH of your seven-gallon fish tank. They do best in acidic waters, so keeping them at a low pH level between four-point five and six-point eight is good.

It would be best to keep the water temperature around seventy degrees, which is a comfortable level for them. In addition to that, you should make sure that your seven-gallon tank has proper filtration and aeration system because cardinal tetras are sensitive to being in stagnant waters.

Regular Water Changes

Regular water changes are a must when it comes to keeping cardinal tetras in a seven-gallon tank. You should do about twenty percent of the total volume every week to ensure that your fish have enough fresh and clean water.

It is also necessary because these fishes tend to produce more waste than other species, which means you will need extra filtration and aeration.

Lights And Decorations

Cardinal tetras do well with regular lighting, which means that you can keep them in a seven-gallon fish tank without any additional light source. However, if the water is not as straightforward as it should be and your cardinal tetras feel stressed out. Adding some extra glow to your aquarium will help make things easier for these fishes.

As for the decorations, you should add a lot of plants to your seven-gallon tank. This will ensure that there are enough hiding places for these fish. It will also help them feel more comfortable in their new home.

Suitable Tank Mates For Cardinal Tetras

There are several species of fish you can keep in a 7-gallon tank with the cardinal tetra population. But there are also some fish types that you should never put in a small aquarium like this one. So what are the suitable tank mates for cardinal tetras?

Good tankmates: Corydoras Catfish, Otocinclus Catfish, Silver Hatchet Fish (Silver Arowana), Male Betta fish. All of these species can work well with cardinal tetras without causing problems among each other.

Avoid keeping these types of fishes with your cardinal tetra population: Guppies, Platys. These species will not work well in a seven-gallon tank because they grow too big and become aggressive towards the smaller cardinal tetras. In addition, guppies will eat any small fish that can fit inside their mouth, including Cardinal Tetras.


In conclusion, the answer to how many Cardinal tetras a tank can adjust is not as simple as most people think. Many factors come into play when determining how much fish you can have in a tank.

The safest bet for keeping your pet healthy and happy is taking the time to research before buying them.  You should prepare yourself and know how much space they need and what you can have in your tank.

Keeping these things in mind, you can figure out the number of fish that can fit into a particular sized aquarium. This will also help keep all the fish safe, healthy, and happy for years to come.