Why Is My Cardinal Tetra Not Swimming? Shocking Causes And Solutions

why my cardinal tetra is not swimming

Cardinal tetras are small fish that may look like neon tetras. There is a small difference between both species but what makes them different is their presence in the aquarium. Such tetras may sometimes stop swimming at all in the aquarium. Why is my cardinal tetra not swimming then? Let us find out.

Cardinal tetras as neon tetras may suffer from swim bladder disease. These tetras are colorful and require the best water parameters to survive as well as thrive in the aquarium. So, you have to make sure to maintain the proper water parameters, give them a proper diet, and keep the tank environment as close to their natural environment as possible. 

Now,  moving forward we will find out the basic causes and solutions we can apply to those problems in order to make the cardinal tetras thrive in the aquarium.

Why Is My Cardinal Tetra Not Swimming?

When a cardinal tetra is having some health issues, it may not swim as much as it used to. Moreover, cardinal tetras seem to come up to the surface to breathe air. This is not a healthy sign. Either they may be ill or they are not able to breathe. So, why do such situations occur?

Look at the following reasons that can cause your cardinal tetra to become more inactive in the aquarium than expected.

Tank Water Cycle

The tank water cycle refers to the nitrogen cycle of the tank. The tank water goes through a series of cleansing processes to maintain a certain oxygen level. Since the tank is smaller than the natural habitat, it needs our help to get the nitrogen cycle going.

If the ammonia, nitrate, or nitrite level rises a lot, then the cardinal tetras find it difficult to breathe. In fact, several diseases might take your cardinal tetras into account. Hence, the tank water cycle is also a reason why your cardinal tetras may be inactive in the tank.

Wrong Water Parameters

Cardinal tetras require a proper water parameter to thrive in the aquarium. It is essential to maintain a proper environment for any living being to be able to maintain a healthy lifestyle. In case such conditions are not met, the cardinal tetras may lose their color.

Even worse, cardinal tetras start hiding and not swimming in the aquarium. A smaller tank can cause such issues as they are already living in an artificial environment. The best thing to do here is to maintain a proper water parameter.

Poor Diet

If your cardinal tetra is having a poor diet, it is not strong enough to fight away the diseases. Similarly, it cannot restore the energy it needs in order to thrive in the aquarium.

It can also cause your cardinal tetra’s bladder to bloat. It might even be the case that you are feeding it properly but the other tank mates take over the food that you are putting in for the cardinal tetra. This can be the cause of the cardinal tetra not swimming in the aquarium.


There are a lot of factors that can cause stress in the tank including the wrong parameters and diseases. In addition, if you have paired your neon tetra with some bad tank mates, it is possible that they fear for their lives.

In such a case, they will hide and be still because of the fish stress. They will not be able to roam around in the tank as freely as they would want to.


Various diseases can occur in the tank if you are not careful enough. Such diseases are communicable too. Thus, you must be careful to catch the symptoms of the diseases so that you can minimize the risks of the loss of your beloved pets.

Such diseases cause the cardinal tetras to be still and lacking in energy. Swim bladder disease is the most common among all which can cause such problems of inactiveness.

External Factors

External factors are the factors that you are putting in the aquarium. This can be different equipment that causes a high flow in the tank water or even just simple things like excessive lighting. Such factors stress the cardinal tetra causing it to lose its color and become more stagnant.

Genetic Factors

Like other species like neon tetra, you may also find that the cardinal tetras have a genetic disorder. Ever wondered that you are doing everything you possibly can but still not being able to make your cardinal tetra comfortable? As an aquarist and a pet owner, this might stress you.

However, it may not be your fault. The problem is that since most people want certain traits in their pet fish, they create such a need to breed the fish in their own pattern. It causes genetic deformities in your fish which makes it more inactive.

What Do I Do To Keep My Cardinal Tetra Active and Healthy?

The above reasons provide you the solution of what you can do differently to make your cardinal tetra more comfortable in the tank system. However, let me tell you a fact that cardinal tetras are not as active as other tetras naturally. So, do not expect it to be overly active too.

In contrast, you must be worried only if they have no activity in the aquarium or seem puffed for some reason.

Maintain The Proper Water Parameters In Tank

You should maintain the following water parameters to make your cardinal tetra happy and healthy.

The Temperature of the tank water 73 degrees Fahrenheit to 81 degrees Fahrenheit
The ph of the tank water 5.0 to 7.5 (Below 6.0)
The hardness of the tank water 2 dGH to 6dGH

Maintenance of Tank Water Cycle

Next in line is the maintenance of the tank water cycle. The nitrogen cycle needs to be taken care of. The ammonia must be zero as well as the nitrate levels must be completely zero. Likewise, nitrite levels can be a maximum of 10ppm.

To maintain the water quality, you may change the water as often as every two weeks. In addition, such changes should be 20 to 25 percent of the total tank water. This helps in regulating the nitrogen cycle of the water.

Spot and Isolate Diseased Fish

Most often, when a fish gets sick, it passes the disease on to other fish in the tank. To avoid such circumstances, you must be able to spot as well as quarantine such diseased fish. Put the sick ones in a separate tank, and feed them appropriately.

Furthermore, you can check which diseases it is suffering from. Then, move forward to the treatment with chemicals or medicines.

Choose The Correct Tank Size For Appropriate Space

The correct size of the tank depends on the number of cardinal tetras you are trying to put in your aquarium. It also depends on the tank mates you put in with the cardinal tetra.

However, supposing you are putting a school of 4 to 6 cardinal tetras in your tank, you need a tank size of 10 gallons. Besides, this will help you to give them the best space to swim around freely without much disturbance. Similarly, you can always add a gallon of water for one cardinal tetra addition in your tank.

Feed Cardinal Tetras Good Diet And Nutritious Food

Since the cardinal tetras are colorful species, you need to take extra care of their health. If you do not feed them a proper diet, they will lose color and get sick. So, make sure you feed your fish with an appropriate and nutritional diet.

In such a case, your cardinal tetra will be healthy and will be able to fight off diseases. However, you must take into account that you shall feed them only twice or thrice a day. Similarly, only feed them as much as they can eat in two minutes.

Schooling Cardinal Tetras

Cardinal tetras are also schooling fish. So, if you put cardinal tetras in a group of five to six, then you are doing great. Of course, the more the merrier. However, you will have to create a better space for the tetras of higher groups.

Putting In Good Tank Mates

You can also add good tank mates for cardinal tetras such as black skirt tetras, gouramis, guppies, ember tetra, chili rasbora, etc. Such good tank mates help to decrease stress levels on the cardinal tetras. To boost its morale, you may even add the upper fish.

Similarly, you should avoid large fish like angelfish, oscar, etc which can prove to be aggressive to reduce stress and increase peace in the tank.

Find out more on our related articles:

External Factors

Fluctuations in the tank environment may also cause the cardinal tetra to become inactive. Slight but sudden changes in the water temperature, oxygen drops, etc can cause the cardinal tetra to remain still.

Similarly, a big filter such as canister filters causing the water flow to be more current can also cause such behavior. Besides, you should also lower the lighting as they prefer to live in black water. You might add some dead leaves to the plant to replicate their natural environment.

Thus, you should put in an appropriate heater and filter to get the cardinal tetra comfortable in the tank.


Plants and decors are the way to make the tetras happy. The cardinal tetras love places to hide. It makes them feel safe. Thus, you can add up some PVC pipes, plants, and various leaves in the tank.

Not only does it make the tank look beautiful, but it also helps to keep your fish healthy and happy. Some best plants can be floating plants like Anubias, Java Fern, Amazon Sword, etc.


The substrate is also a major part of the aquarium. You have to put in two jars of water for one handful of substrate for a couple of days to see some difference in the pH of the water. If the ph has been changing, it might be a reaction to your tap water.

Furthermore, you should test the water for 24 hours before putting in any fish. Check the pH of the water before putting it in fish. You can use fine sand as a substrate.

Frequently Asked Questions

Are Cardinal Tetras and Neon Tetras The Same?

Cardinal Tetras and neon tetras are quite different. Even though they appear similar to each other in appearance, the cardinal tetras have a different water parameter requirement than that of the neon tetras.

The cardinal tetras have higher shades of red than that of the neon tetras. Similarly, the neon tetras are more active than that of the cardinal tetras.

How Can I Tell If My Cardinal Tetras Are Sick?

Any sick cardinal tetras will show the following warning signs:

  • Being inactive
  • Swimming to the top for the search of oxygen
  • Swimming upside down
  • Being more aggressive
  • Small accidents with other fishes
  • Swimming irregularly in the tank
  • Bloated body
  • Not responding to food or not eating at all

What Kind of Substrate Do You Put Cardinal Tetras In?

Cardinal tetras are middle dwellers in the aquarium. However, it does not mean you do not need any substrate in your aquarium. Thus, you can use fine sand as a substrate so as to imitate the natural environment it lives in.

This is also perfect for other live plants which you will definitely need as a decoration. Moreover, it is also the best substrate for any kinds of bottom dwellers fish you may use in the aquarium.

Last Words

There are various aspects that can cause your cardinal tetra to be inactive and not swimming. You can be attentive to find out the exact problem and then take steps to solve the problem. The attempts will help you to become the best owner and aquarist to your beloved cardinal tetras.

Make sure you understand their needs and create the best natural environment for them as you possibly can. Happy fish keeping!

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