Ideal School Size For Cardinal Tetras: Let’s Find Out!!

Cardinal tetras are social and friendly fish that enjoys company. Moreover, the tank must contain an ideal number of Cardinal tetras for a healthier and happier life due to the schooling nature. So, what do you think might be an ideal school size for Cardinal tetras?

The ideal school size of Cardinal tetras can be anywhere between six and nine fish, depending on the kind of environment you want to create in your tank. When fewer than five or more than ten cardinal fishes are in a group, they tend not to swim around as much since their instinct is to stay away from the bigger groups.

Moreover, suppose there are more than ten fishes in a single group. In that case, it is hard to monitor the behavior of every individual fish, thus increasing the chances of diseases and injury.

This article will discuss the ideal number of Cardinal Tetras for a school and why it is crucial to have a perfect size.

What Are Schooling Fish?

Schooling fish are those that like to live in groups. There’s safety in numbers for these little guys, and they tend to fare much better when kept with their kind instead of as a single specimen or pair among other species. They also will be more comfortable and thrive under the right conditions (we’ll get into those later).

There are many different species of schooling fish, but one of the most popular for home aquariums is probably the cardinal tetra. These little guys like to swim in schools together and look stunning while they do it! They’re easy to care for (more on that soon), making them great beginner fish, as long as you can give them the right conditions.

What Is The Ideal School Size For Cardinal Tetras?

The best school size for cardinal tetras would be six or more. Moreover, this is because Cardinal tetras are schooling fish and need to have others of their kind around them to feel comfortable, but avoid keeping too many together because they can get irritable without enough room to swim freely.

However, if you keep more than ten cardinals, you might find them nipping each others’ fins, as some cardinals can be pretty aggressive. On the other hand, if you have fewer than this number living together, the left out once might feel stressed and even die.

Naturally, it would be best to purchase six or more when you first set up the tank. It helps Cardinal tetras establish their community and feed on their natural food sources instead of competing.

Still, if you opt for lesser or less than six cardinal tetras, you should be extra attentive and conscious to ensure their comfort and safety.

Why Is It Important To Keep Ideal School Size Of Cardinal Tetras?

Cardinal tetras are schooling fish, and they will feel more comfortable when in groups. When you talk about ideal school size, it is crucial to have the correct number of fish in the tank to keep them lively and avoid overcrowding.

Some of the reasons why it is crucial to keep Cardinal tetras of ideal school size are:

Less Aggression:

Small schools of cardinal tetras reduce aggression towards one another. Thus, it ensures that none feel stressed or injured. It also keeps them healthy since you do not subject them to unnecessary stress and injuries. Besides being less aggressive, this species does not show much aggression against other fish in their tank.

Better Water Quality:

Cardinal tetras are very sensitive to poor water conditions, and punctuation in water parameters can easily affect them. Therefore, keeping a small school of cardinal tetras will help avoid overcrowding in the tank. But, on the other hand, it would cause stress and injuries, especially when it comes to territorial behavior such as defending their territories from other fishes or against each other.

Better Predator Defense:

Cardinal tetras are among the smallest fish species in aquariums. Cardinal tetras can feed on small insects, high-protein food like larvae, brine shrimp, tubifex worms, etc. But, unfortunately, it makes them an easy target for larger fish predators.

Large predator tankmates are less likely to eat the small schools of cardinal tetras. So, this reduces the risk of injury or death incurred during fights with other fishes in the aquarium. It also prevents wiping out of your small school hence, avoiding stress and trauma from the loss of their schoolmates.

Less Disease:

Cardinal tetras are not immune to diseases. But stress and overcrowded aquarium setting can easily affect these fish. Small schools of cardinal tetras reduce stress, injury, and death risks that may lead to disease outbreaks within your tank. It also helps you avoid making your cardinal tetra fish suffer from the trauma of losing their schoolmates.

Better Feeding Habits:

Cardinal tetras are small in size, and they need to eat frequently to survive. Keeping a large school of cardinals can reduce feeding time since there will be many fish-eating at once. Thus, it helps in preventing them from starving because of a lack of food. Keeping small schools of cardinal tetras will ensure that they have enough to eat, making them healthier, stronger, and more active in the aquarium.

Better Coloration:

Cardinal tetra fish have vivid colors which become duller if not appropriately fed or stressed out because of smaller schools of cardinal tetras. But, on the other hand, small Cardinal Tetra schools will help them develop brighter colors since they do not feel stressed out. Thus, it helps in ensuring the health and well-being of Cardinal tetras.

How To Keep A School Of Cardinal Tetras Happy And Healthy?

A school of cardinal tetras is a beautiful addition to any tank. But there are some essential things you need to know before adding them. Before we get into the specifics of how many cardinals you can keep in an aquarium, let’s go over some basics first.

Ideal Number Of Fish In Tank:

The number of Cardinal tetras you can keep depends on the size of your tank. You can select the right number of fish by:

Ideal Number Of Cardinal Tetras= Tank Size (in gallons)/ Size Of Cardinal tetras (in inch)

An important rule to follow is that you should never overcrowd fish in an aquarium. When a fish’s home (the aquarium) becomes too small, it suffers from stress and can become very sick. Similarly, when the tank is too large, they feel lonely and want to interact with others.

Maintain An Ideal Temperature And pH:

The ideal temperature for Cardinal tetras is between 72 and 82 degrees Fahrenheit. But this may vary depending on the species. So please make sure you check your particular variety to ensure they can tolerate such a wide range of temperatures.

You should also maintain an appropriate pH level in the water for your fish. The ideal pH range is between 4 and 6, but this may vary depending on the cardinals you are keeping.

Regularly Change The Water:

You need to change out a quarter of the tank’s water every week. Be sure that it matches your current water’s temperature and pH level not to shock your fish when you add new water.

Also, make sure to clean your tank regularly with a water conditioner and some safe aquarium rocks. It will help keep the tank looking beautiful for years.

Keep Ideal Ratio Of Male And Female Cardinals:

Keeping too many males or females can be problematic because they will fight with each other. The ideal ratio of male to female cardinal tetras is one to three. But the exact number may vary depending on your tank size and how well you can keep them separated.

Give Them A Healthy Diet:

Cardinal tetra fish should eat various foods, including flake food and frozen or live brine shrimp. In addition to these staples, they may sometimes eat small worms and insects found in the tank for a little extra protein.

Make The Tank Lively:

You should also add some live plants and other decorations to your tank. It will help the cardinal tetras feel at home. It also give them a sense of security to interact with one another more freely. Some of the decorations for the ideal tank are Driftwood, Rocks, Live Plants, and a few artificial plants for more variety.

It is important to remember that you should never use any chemicals or additives in your tank as these can be harmful to the fish.


In conclusion, it is tough to pinpoint what the perfect school size for cardinals might be. However, we recommend that you keep groups of six or more. It will make your fish happier and allow them to interact with each other when they are not busy swimming around in their tanks.

If you have a group of fish that is smaller than six, you should monitor them carefully. First, it helps to make sure they are not acting aggressively towards each other.

When you keep these tips in mind, you’ll be well on your way to keeping Cardinal Tetra fish that are happy and healthy.

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