Are Five Cardinal Tetras Enough? How Many Cardinal Makes A School?

Cardinal tetra fish is a beautiful and popular tropical species. You can find these fish in most pet stores across the world. Their bright colors, hardy nature, and small size have made them staple community tank residents for years. However, most hobbyists keep tetras with other similar species, so it’s easy to wonder: are five cardinal tetras enough?

No, five Cardinal tetras are not enough. Since they enjoy living in groups of at least six, you need eight total to have the minimum amount for a school. You also need more if your tank is more significant than 20 gallons because this means you would only have one fish per ten gallons, and that wouldn’t be fair or healthy for them.

If you are planning to keep a Cardinal tetra, then this is an important question to consider. So, this post is all about Cardinal tetras and their specific needs.

What Type Of Fish Is Cardinal Tetras?

Cardinal tetras are small freshwater fish often used in aquariums. They can be three inches long and called Cardinal tetras because of the red stripe that runs along each side of their body.

They come from South America, where they inhabit slow-moving rivers and streams. These habitats typically have thick vegetation. The fish will gather in groups to feed on insects and other tiny bits of food that fall into the water.

Are Five Cardinal Tetras Enough?

You should not have only five cardinal tetra fish in a tank because they may become aggressive and end up killing one another. So it’s best if you have around ten or more of them at the same time.

Cardinal tetras are schooling fish, and they need a lot of others to play with. They don’t do well in small groups, so having five or fewer would not be suitable for them at all. They need to be in a school of at least six or more. It’s best if you have ten, but they could survive with five.

In the schooling group of Cardinal tetras, there must be at least two males and three females. They show aggression towards each other if there isn’t the right amount of males and females present. If you notice that they aren’t getting along, then you should invest in more fish at once to meet all their needs adequately.

Is it okay to have five cardinal tetras?

Yes, having five cardinal tetra fish is fine if you only plan on keeping them in the tank for a short time. However, it would be best to keep these fish by themselves because they are sociable and like living with other members of their species.

They also need at least 25-30 gallons of the tank with proper filters, air pumps, lightings, plants, and non-aggressive tanks to live happily.

How Many Cardinal Tetras Should You Keep In A Tank?

The number of fish that you must keep in the tank depends on many factors. These factors include:

Size Of The Tank

One cardinal tetra per gallon is a good rule to follow if you want them all to be happy. This means that these fish will have enough space to move around without bumping into each other or hanging out near the top of the tank where they cannot breathe.

Other Fish In The Aquarium

If you plan on keeping other fish in the tank with your cardinal tetras, make sure that these other fish are not very aggressive or extensive. If they attack your cardinals, they will starve for food and die without enough room to move around. Also, it would be best to avoid any small species such as neon gobies, emerald dwarf rasboras, pygmy cories, and others.

Types Of Filters

The type of filter you are using will also affect how many cardinal tetras you can keep in your tank. You should have at least one gallon for every ten gallons of water so that the ammonia does not build up to dangerous levels. If there is no filtration, it would be best if they did not stay in the tank for very long.

For a long time, most aquarists assumed that the minimum number of cardinal tetras should be at least six. This is because experts believed that they must have one male and five female Cardinals to breed successfully.

However, this rule does not apply to all types of Cardinal Tetras. For example, some types are more likely to cause problems if you keep them in small groups.

What Is The Ideal Tank Size For Cardinal Tetras?

The minimum size tank that you should get for a school of cardinal tetras is 20 gallons.

While the ideal situation would be to have 30+ gallons, if you are keeping them in something smaller than 20, then at least make sure that they all have their territories and hideouts to avoid each other if need be.

There must be adequate space with live plants, decorations, filters, and of course, the substrate to allow these fish their favorite activities (such as digging and hiding). Cardinal tetras are active fish that need to constantly move around their environment, swimming against the current of the water.

If you are keeping them in an aquarium that is smaller than 20 gallons, then at least make sure they have enough space to swim back and forth without feeling confined or suffocated by any objects.

What Will Happen If There Aren’t Enough Cardinal Tetras In Tank?

If you find that your tank is not getting enough cardinal tetras, a couple of things could happen. Such as:

  • The cardinal tetras will feel anxious and stressed, which could cause them to have decreased appetites. This means they won’t be as active as usual, so you’ll probably notice a decrease in their energy levels.
  • If the tank is not getting enough of any species, there may not be an adequate amount of biological filtration. This can cause ammonia levels to be too high, which will poison your fish, so it’s important to have enough cardinal tetras for them to eat.
  • Breeding becomes challenging without enough cardinal tetras in the tank. Each female has a higher chance of laying eggs and successfully hatching them when enough cardinal tetras are in the tank.
  • Cardinal tetras are schooling species, so they prefer to be in a group of at least three fish. If there aren’t enough cardinal tetras in the tank, they’ll feel stressed because other species will bully them.

What Are The Consequences Of Overcrowded Tank?

Maintaining a balanced ecosystem is vital to the health of your fish. However, when you have too many fish in one tank, you can run into problems. Some of the consequences of overcrowded tanks are:

  • The fish may fight with one another for space, food, and oxygen. As a result, they feel stressed out, which can lead to disease.
  • Fish waste will build up in the tank because there isn’t enough water flow around the aquarium to carry it away – this is not good for your health or theirs.
  • If you have too many Cardinal tetras together, they may become aggressive and nip at the fins of other fish, even your hands.
  • In an overcrowded tank, the water quality can decrease, and there will be a need to change it more frequently.

If you’re thinking about adding Cardinal tetras to your aquarium, make sure that you’ve selected an appropriate tank size for them first.


Q: Will I Be Able To Keep Five Cardinal Tetras In My Aquarium?

A: As long as you provide them with suitable living conditions, it is possible. It will not only avoid stress for the fish but also reduce your work of caring for them. But only five Cardinal tetras is not enough for a community aquarium. You need to be aware of the water parameters, like temperature and pH.

Q: Will Five Cardinal Tetras Fight?

A: They may become aggressive towards each other due to a lack of enough space for establishing their territories. This can cause stress for them, which will lead to death in some cases unless you act fast.

Q: How Do I Keep The Water Parameters Stable?

A: First of all, you need to know about the temperature and pH level. The recommended temperature is 74°F-80°F or 23°C-26°C, and the pH range should be between 4.6 and 6.2, which will ensure your fish’s health. Also, change the water regularly to avoid the build-up of harmful substances.

Q: How Many Cardinal Tetras Do I Need?

A: There is no particular number of cardinals that you must have in your tank, but there are some factors to consider when deciding this matter. A general rule would be one male and three females per aquarium for breeding purposes.

However, if you wish only to keep them as pets, one male and four females would be a good option. Just make sure that you have enough space for each cardinal tetras to thrive in your tank.


By looking at these points, you can see that five cardinal tetras are not suitable for keeping them in your aquarium. There is no way they will be able to survive together or reproduce, for that matter. So if you want a school of cardinals in your tank, make sure about 20-30 individuals live in your tank.

Although five cardinal tetras are okay to have in your aquarium, they might not be the best choice. Hopefully, this article gave you all the information that you need.

Thank you for reading the blog post. We hope you enjoyed it.

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