How Many Cardinal Tetras Can I Put In A 2.5 Gallon Tank?

Cardinal tetras are magnificent fish with vibrant colors. Moreover, these fish can live pretty well in limited environmental conditions, making them a popular fish among aquarists. Although these fish are easy to take care of, do you think they can do well in a smaller tank? How many Cardinal tetras can you put in a 2.5-gallon tank?

Cardinal tetras are small freshwater fish, so they do live in a 2.5-gallon tank. You can keep around one to three Cardinal tetras in a tank this size. But, you have to remember that they are very active fish. So, it might be difficult for them if there is not enough space in the tank.

In this post, we will discuss Cardinal tetras, their tank size, and many more. But, before that, let us know about cardinal tetra.

What Is a Cardinal Tetra?

A cardinal tetra is a tropical freshwater fish that gets its name from the striking red color on its bodies. Cardinal Tetras are small, peaceful fish that are best in schools of six or more. It helps to ensure they are not anxious when you leave them alone. They look great when housed with other brightly colored species like neon tetras and guppies.

Cardinal tetras originated from the Amazon River in South America. They are native to blackwater tributaries, which have a dark tea coloration due to the humic acids that leech into the water from decaying vegetation on river banks.

The cardinal tetra is an egg-scatterer and prefers slightly soft, acidic waters with lots of leaf litter at the bottom. They are not fussy about water conditions but will be more colorful in acidic water.

What Is The Ideal Size Of Cardinal Tetras?

The ideal size of a cardinal tetra is around two inches. As for the number, you can put anywhere from five to ten in a tank no bigger than 25 gallons. If anything, putting more will provide your fish with better company and entertainment as they swim back and forth throughout the water column.

Moreover, the size of Cardinal tetra also depends on the environment they live in and their species. For example, cardinal tetras living in the wild tend to grow larger than those living in an aquarium.

Can You Keep Cardinal Tetras In A 2.5 Gallon Tank?

Yes, you can keep cardinal tetras in a tank that is around two and a half gallons. They are among the most popular tetra species because they can tolerate lower water quality than other tropical fishes, making them perfect for tanks with smaller biological filtration systems.

But if you want your Cardinal tetra to live a longer and happier life, you should increase the volume of your tank. Use a bigger tank with good filtration, heater, lighting, and decorations are always better.

What Is The Best Cardinal Tetra Tank Size?

A minimum of 20 gallons is necessary for cardinal tetras to thrive, but the bigger the tank, the better it will be for their health and happiness. It can live in a school, so you should keep at least six individuals together to prevent them from being lonely or stressed out.

A school of cardinal tetras will need a tank at the very least 30 gallons, but if you are only planning to keep one or two, they can survive in smaller tanks. This fish needs room to swim around and play with other fish, so it’s not a good idea for bowl-shaped aquariums like betta bowls because they don’t have a lot of room to swim around.

How Many Cardinal Tetras Can I Put In A 2.5 Gallon Tank?

In a ten-gallon tank, you can have up to eight cardinal tetras comfortably. In a five-gallon aquarium, the count will be five maximum. Anything beyond that and your fish will feel very cramped in their living quarters which is not healthy for the long term.

Some owners do keep about two to three Cardinal tetras successfully in a 2.5-gallon tank. But the fish will not live for long in this kind of setup. A cardinal tetra needs a little space with enough plants, decoration, and some tankmates to live happily.

Since a 2.5-gallon tank fails to give such an environment, your fish will feel stressed, and they may even suffer from fin rot. Thus, keeping Cardinal tetra in a smaller tank below five gallons is not a good idea.

What Are The Problems Of A Smaller Tank?

Tank size plays a vital role in the health of Cardinal tetras. So, when keeping the fish in a smaller tank has lots of risks.

Some of the problems of the smaller tanks are:


Cardinal tetras are schooling fish and prefer to live in a group of six. Unfortunately, when you keep six fish in a 2.5-gallon tank, the tank becomes overcrowded. As a result, all the fish won’t get enough space to move around and swim.

This situation won’t allow the fish to grow and thrive. So, overcrowding is one of the biggest problems of a smaller tank.

Unsuitable Water Conditions

Your cardinal tetras will face many water condition issues if you keep them in a small tank, like fluctuating temperature levels, unsuitable pH values, and high levels of ammonia, etc.

Water condition issues will affect your fish’s health and cause many problems like stress, disease, and even death. So, the smaller tank doesn’t provide suitable water conditions for cardinal tetras to live a healthy life.  

Short Water Cycle

Cardinal tetras require a high level of cleanliness in their water. Therefore, keeping them in a small tank won’t provide the fish with enough time for the water cycle.

The smaller tanks don’t have the more extended filter and filtration systems that regularly remove harmful chemicals from your cardinal tetras’ water. It will not allow the toxicants like ammonia or nitrites to get rid of them from the water.

Not Enough Oxygen

Cardinal tetras are susceptible fish that require a large amount of oxygen to live happily and healthily. If you keep them in a small tank, it won’t provide the fish with enough oxygen.

Smaller tanks don’t have sound water circulation systems that can put more air into your cardinal tetras’ water and give them sufficient oxygen levels.   

What Are The Requirements For A Ideal Cardinal Tetras Tank?

Cardinal tetras are easy-going fish. They do not require much to live happily in the tank. However, a few of their tank requirements are:

Tank Size

There will be an optimal range for the tank size. But if you are thinking of having a small community, your cardinal tetras should have at least 20 gallons (75 liters) space to swim around.

Water Parameters

Cardinal Tetra is not picky about its water parameters; it can adapt quickly, even slightly acidic or alkaline water. But, if you want to keep them in the long run, make sure that your water parameters are not too extreme (too acidic or alkaline).

Water Temperature

You should maintain the temperature within 24-26 degrees Celsius. Anything above this will stress out your fish and might even cause death.


Since they love to swim in the middle region of the tank, make sure that there are some light sources at the top. Also, do not expose your tank to direct sunlight for too long; it will affect their behavior and coloration.

Live Plants And Decorations

Cardinal Tetras love to hide in the dense vegetation. So, make sure that there are enough live plants and decorations for them. However, keep an eye out on your fish when they start digging up or chewing on the tank decor.


Keep a few other fish species with your cardinal tetras, but make sure that they are not too small or aggressive. Cardinal Tetra might be peaceful by nature, but it can still nip the fins of their tankmates if provoked.

Important Note: Make sure that you do not overcrowd your tank because this will stress out your fish and may cause them to die due to the low oxygen levels.

Some FAQs

What Are The Best Foods For Cardinal Tetras?

Cardinal tetras are omnivorous fish. They can eat both meat and plant foods. However, it would be best to supplement their diet with a variety of live food such as brine shrimp or mosquito larvae to keep them healthy and happy in the tank. You can also feed them sinking wafers and flakes that fall to the bottom of your tank.

What Is The Right Temperature For Cardinal Tetras?

The right temperature for cardinal tetra is 70-81 degrees Fahrenheit, as they come from tropical regions in South America such as Brazil and Guyana, where there are warm temperatures year-round. You can keep them at higher or lower temperatures, but their metabolism will slow down, and they won’t be as active.

What Are Some Cardinal Tetra Diseases?

Many diseases can kill cardinal tetras, such as fungus infection, bacterial infections, parasites, or protozoal infestations. Tank-bred fish don’t have the immunity to fight off these pathogens as wild ones do. Therefore, they are more susceptible to diseases in the aquarium.


In conclusion, a cardinal tetra can live in a tank with other fish so long as they have plenty of space and some hiding places. The number of cardinal tetras that you put into your aquarium will depend on the size, shape, and volume of water available for them to swim around in.

If you want more than one or two, then make sure you have a tank of at least six feet in length. Unfortunately, it is not always easy to find cardinal tetras for sale. But if you keep an eye out and search online, you might be able to get the one you want.

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