How Many Cardinal Tetras Can I Put In A 15 Gallon Tank?: Tips and Tricks

Cardinal tetra fish is a small freshwater tropical fish that can live in both communities and planted aquariums. However, unlike typical water conditions and some plants, Cardinal tetras do not need to live happily in a tank. So, do you think a 15-gallon tank will be perfect for them? How many Cardinal tetras can I put in a 15-gallon tank?

Cardinal tetras are small fish, so that they can do perfectly fine in a 15-gallon tank. But the number of Cardinal tetras that you can put in that tank depends on the size of the fish, water conditions, tankmates, and decorations.

The maximum number of Cardinal tetras that you can put in a 15-gallon tank is six Tetras because this will provide your fish with enough room to swim around freely. However, you should always avoid overcrowding the fish as it may cause stress leading to illness or even death for them.

If you are new to fish keeping, this post is a guide for knowing more about Cardinal tetras. I hope you will enjoy it.

Can I Put Cardinal Tetras In A 15 Gallon Tank?

Yes, Cardinal tetras can live in a 15-gallon tank. As long as you have a larger tank, there is usually no problem putting in cardinal tetras. They can be quite beautiful to watch and very hardy fish that are easy to care for.

Thus, it’s always important to know what types of fish work together and their size before adding them to a tank. It’s also important to make sure the fish are compatible with each other and not fight or harass one another too much over food, etc.

Which Size Of Tank Is Best For Cardinal Tetras?

Cardinal Tetras do well in groups of six or more prominent, so you will need at least a 30-gallon tank to house them. This should be the smallest tank that you use for your Cardinal Tetras. You want to avoid keeping them alone because they are very social and like living with other cardinal tetra fish and their species.

You can keep them in a 20-gallon tank, but you will want to ensure that there are at least six cardinal tetras. They do much better when living with their kind and in larger groups of six or more.

How Many Cardinal Tetras Can I Put In A 15 Gallon Tank?

There is a lot of debate on how many cardinal tetras I can put in my 15-gallon tank. Some people will say that you should only have one or two per fish, and others will tell you to fill your tank with as many as possible. Well, the truth lies somewhere in between.

Usually, most aquarists recommend keeping about five to six cardinal tetras in a 15-gallon tank. However, some beginner aquarists have done well with keeping up to ten of these beautiful fish in the same size aquarium. Just follow some simple tips like:

  • Regularly change the water in the tank.
  • Monitor your water chemistry to make sure it is safe for all of the fish in the aquarium.
  • Use a good filter that will keep up with removing waste from the tank and maintain oxygen levels at an appropriate level to ensure optimal health for all of your cardinal tetras.
  • Maintain optimum water parameters with temperatures of 78-82 degrees Fahrenheit and a pH level of around six.
  • Please keep them in groups and ensure that the tankmates are peace-loving.
  • Always provide them with plenty of live plants and hiding places. It is because they do not like disturbance or exposure to other fish that are more aggressive.

Do these simple tasks. You will have beautiful groups of cardinal tetras flourishing in your aquarium for years to come.

What Determines The Number Of Cardinal Tetras In A 15 Gallon Tank?

As I mentioned above, the number of cardinal tetras you can keep in your tank depends on various elements. Such things are:

Size Of Cardinal Tetras You Keep

The first and most important one is the size of your cardinal tetras. The bigger the fish, the more room you will need in your aquarium for them to thrive and survive. Thus, for a tank of 15 gallons, Cardinal tetras must be of a size no less than two inches. However, if the size of Cardinal tetras increases, then their number needs to decrease.

The Number Of Other Fish You Keep

Another important factor is the number of other types of fish you keep with your Cardinal Tetras. The amount of space a tank can provide for each type will determine how many cardinal tetras it can accommodate. If more than one species share the same aquarium, you need to reduce their numbers accordingly or increase the size of the tank.

Temperature Of The Water

The water temperature is another factor that determines how many cardinal tetras your 15-gallon aquarium can hold. If you keep tropical fish, you need to maintain a warmer and stable environment for them inside your tank. On average, it should be around 80 degrees Fahrenheit, but this varies depending upon the type of fish.


Even though Cardinal Tetras commonly live in dark places, this doesn’t mean they do not need any lighting inside your tank. On the contrary, a simple light source might even help them thrive better and grow faster! However, if you keep more than one species together, make sure their respective lights don’t cause any disturbance.

Plants And Decorations

A 15-gallon tank needs to provide your cardinal tetras with enough space to swim around. Thus, it would be best if you kept in mind that they might sometimes stick in between any plants or decorations inside the aquarium and suffocate. Therefore, make sure your Cardinal Tetras have enough hiding spaces in the form of plants or rocks for them to feel safe and secure.

What Are The Pros And Cons Of Keeping Cardinal Tetras In A 15 Gallon Aquarium?

Cardinal tetras are the most easy-going fish to keep in your tank. However, if you decide to keep your fish in a 15-gallon tank, you must be familiar with its pros and cons.


  • Frequent water changes
  • They are one of the easiest species of fish to care for.
  • They are peaceful.


  • It is easy for cardinal tetras to intimidate other fish, timid ones that need lots of hiding spaces and plants, not to feel stressed all day long.
  • Their size makes them a popular target for more aggressive and predatory fish like bettas.
  • Their size makes it difficult to add any other species of peaceful tank mates except some smaller tetras or danios, which may nip at their fins.
  • They love densely planted tanks with lots of hiding spaces provided by plants and rocks – but this will make it difficult to clean the tank.
  • They are very active swimmers 15 gallons of water is not enough for them. Usually, they need 30 or more gallons per fish if you want your cardinal tetras to be happy and healthy.

What Happens If I Put Too Many Cardinal Tetras In A Tank?

Cardinal tetras are peaceful and can do well when you keep them in groups. But you will face various problems if you keep Cardinal tetras in a tank. Such as:


You need to have at least two gallons of water for every one cardinal tetra that you keep. If there are more than five Cardinal Tetras in a tank, it will be challenging to maintain the balance between vegetation and fish.

Unhealthy Water

It is crucial to make sure your aquarium has enough filtration system or frequent water changes. If your tank does not have enough filtration system, the waste produce by fish will build up very quickly and create an unhealthy environment for them to live in.

Not Enough Plants

It is crucial to make sure your tank has enough plants for the Cardinal Tetras. The reason being that they are schooling fish, and this means that they will feel secure in numbers. If there are not enough plants, the cardinal tetra might become stressed out because of their lack of security.

Competitions For Food

Cardinal Tetras are peaceful fish, but they might become aggressive when it comes to food. If you put too many Cardinal Tetras in a tank together, there will be competition for food, which can cause unnecessary stress.

Lack Of Enough Oxygen

Cardinal Tetras require at least six parts per million of oxygen in the water. If there is not enough oxygen, they will become lethargic and might even die because of lack of oxygen.

Behavioral Problems

If you keep the cardinal tetras in a too-small tank, they might stop schooling together. This can lead to many problems because it will cause them stress when swimming around the tank looking for fish of their kind. It can also cause behavioral issues, which could include chasing other schools or bullying by larger fish.


Summing up, Cardinal tetra is not a very large fish, but it does like to school. They are one of the most common South American freshwater tropical fish that can be present at many pet stores or online shops. Just make sure you do your research on the type of food they eat and other information about them before buying them.

Thanks for reading, and I hope you found this article helpful. For more information, check out other posts on this blog.

Keep fishing!

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