How Many Cardinal Tetras Can You Have In A 1 Gallon Tank?

Cardinal tetras are freshwater fish that comes from South America. They belong to the family of Characidae as Paracheirodon axelrodi. Although some experienced aquarists recommend 30-gallon tanks for this species, keeping them in smaller tanks is still possible. But, how many Cardinal tetras can you have in a tank as small as 1 gallon?

Most aquarists do not recommend keeping Cardinal tetras in the one-gallon tank. This is because the maximum number of Cardinal tetras for the one-gallon tank is one or two. But since these fish are schooling fish, they prefer to live in a group of six Cardinal tetras. Thus, you should better not try to keep them in the one-gallon tank.

Caring for a fish needs some research and information. So, you can prepare yourself through this article. But, first, we will try to answer some of your most common questions about Cardinal tetras.

How Many Cardinal Tetras Can You Have In A 1 Gallon Tank?

In a one-gallon tank, you can only house one or two cardinal tetras. But since these fish are schooling fish and prefer to live in six fishes, the best option is not to go for this kind of school. If you still insist on having them in a one-gallon tank, you should either get a male and a female.

Cardinal tetras are active swimmers. Therefore, you need to have a tank of at least ten gallons if you want your fish not to feel cramped and stressed out. This way, they will live no longer than six months in the one-gallon tank. There are also cardinal tetras that grow up to four inches long, which means their requirement for swimming space is more than just having them in a one-gallon tank.

Cardinal tetras are peaceful fish, and they will not bother other fishes that you put in the same tank with them as long as these other fish do not belong to their species or genus. But in a smaller tank, they feel threatened and territorial, which leads them to attack and kill other fish.

Why Should Not You Put Cardinal Tetras In A 1 Gallon Tank?

Cardinal Tetras are a prevalent fish. Because of their fabulous colors, they can quickly become the focal point of your tank. If you choose to keep cardinal tetra in such small tanks, keep in mind not to keep them there for an extended period.

Being a schooling fish, Cardinal tetras will not do well on their own. A school of six fish will be too big for a one-gallon tank to handle. In a smaller tank, any deviation from the school size will result in aggression among the fish.

Cardinal tetras need space to swim freely and play. Unfortunately, a one-gallon tank does not have the volume to support a Cardinal Tetras school, much less giving them room to play and swim.

You will also need a very efficient filter to keep your cardinal tetra happy and healthy long term. A smaller tank means that the filter cannot process as much water. This means you need to clean the tank more often. 

It is not suitable for anyone to keep cardinal tetras in one-gallon tanks because they are small and pretty. They need space to swim around to do well physically and socially over time. If you only want a few fish, choosing other species that can do well in a one-gallon tank is better.

What Is The Best Tank Size For Cardinal Tetras?

Cardinal tetras do best in tanks of at least 25-30 gallons. However, you can even keep them in much smaller aquariums. They are very peaceful fish and will only work well with other cardinals or non-aggressive tank mates that aren’t too big or active. For example, you could keep them with some corydoras catfish but not with a Plecostomus or goldfish.

In addition, the more tetras you have in your tank, the happier they will be. That would be best if you could provide at least 30 gallons for them to play around, but even a 20 gallon is enough space for six cardinals. No matter what size of aquarium you choose, be sure to keep a lid on your tank, so they don’t jump out.

What Will Happen If I Put Too Much Cardinal Tetras In A Tank?

If you put too many cardinal tetras in a tank, the water conditions will become unstable, and it could lead to stress for your fish.

Some of the consequences of overcrowding a tank with Cardinal tetras are:


If you have a tank with many Cardinal tetras and other fish, the other fish will become stressed, leading to aggression. This can result in fin nipping or even the death of other fishes.

Unhealthy Water

With an overcrowded tank, there is less oxygen available for your cardinal tetras. Since they compete for the same resources and create more waste, this can create toxins in the water. As a result, the water is more polluted in lesser time.

Health Issues For Cardinal Tetras

Cardinal tetra has a labyrinth organ that allows them to breathe air from the surface of the water. If they cannot do so because there is insufficient oxygen available due to overcrowding, this leads to suffocation or even death. This could also cause your cardinal tetras to jump out of the tank.

Filtration System Catches Cardinal Tetras

Since the Cardinal Tetra has long and flowing fins, it is more likely to be stuck in the filters of your aquarium. If you notice this, make sure to check the condition of their fins and clean out any stuck debris from them by using a soft brush or cotton bud dipped in some water.

Cardinal Tetras Stops Growing

Cardinal tetra fish will not grow as large as they would in the wild. This is because of their small tank. They will not get enough food in a smaller aquarium. It leads to stunting in the cardinal tetra fish growth rate.

Competition For Food

If too many Cardinal tetras are in a tank, they will monopolize all the food and starve other fishes. Unfortunately, this can also make them more susceptible to attacks from its predators since it is not getting enough food to keep its energy up.


Can You Breed Cardinal Tetras In 1 Gallon Tank?

No, you cannot breed cardinal tetras in a one-gallon tank. For breeding fish, you must have at least a five-gallon tank.

Can You Keep Multiple Fish In 1 Gallon Tank?

No, you cannot keep multiple fish in a one-gallon tank. With only one cardinal tetra, it is impossible to fit any other fish with the cardinal tetras. This means that if your cardinals die or become sick and need medication, you cannot get other fish to replace them.

1 Gallon Tank Or Fishbowl, Which Is Best For Cardinal Tetras?

A one-gallon tank is not the best option for keeping cardinal tetras. A ten-gallon fishbowl would be a better alternative to a one-gallon tank. However, the one-gallon tank has no filtration system and limited space, leading to poor water quality. Whereas, ten-gallon or more fishbowl provides more area and regular water change facilities.


Summing up, as long as you’re providing a proper environment and diet, then there’s no reason why cardinal tetras can’t live with other fish in one-gallon tanks. And since they are such pretty and active little fishes, I recommend them to any beginner aquarist.

I hope this helps.

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