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Cardinal Tetra Care: Everything You Need To Know

Cardinal Tetra Care: Everything You Need To Know

Knowing everything about Cardinal Tetras before adopting some for your tank will help you take good care of them. Your fish will be happier, healthier, and much more active when you understand what you need to do to help them thrive. 

Cardinal Tetras are peaceful freshwater tropical shoaling fish. They require soft, acidic water between 73°F and 81°F (23 and 27°C). Many people love them for their bright bodies and energy. Cardinal Tetras are also harder to raise than Neons because they’re almost all still wild-caught.

In this article I’ll cover their care, preferred tank set-up, and common health problems Cardinal Tetras can have. There’s much to learn, but it’s always fun! 

Cardinal Tetra Overview and Natural Habitat

  • Common name: Cardinal Tetra
  • Scientific name: Paracheirodon axelrodi
  • Care level: Moderate
  • Size: 1.25 inches (3 cm)
  • Lifespan: Five years
  • Temperament: Peaceful
  • Diet: Omnivore
  • Group size: At least six
  • Minimum tank size: 20 gallons
  • Tank level: Mid-top dweller
  • Water temperature: 73°F to 81°F (23 to 27°C)
  • Water pH levels: 4.6 to 6.2
  • Water hardness: Under 4 dGH

The Cardinal Tetra is a shoaling fish, which means it likes to live in a large group. So, you’ll need to keep at least six in your aquarium for them to feel comfortable. These gorgeous fish are very peaceful and won’t fight other fish. They can be very energetic and a lot of fun to watch.

Cardinal Tetras are tropical freshwater fish native to South America, particularly Brazil, Venezuela, and Colombia. Leonard Peter Schultz, an American ichthyologist, is credited with discovering and circulating these fish throughout South America as pets in 1965.

Today, most pet Cardinal Tetras are still imported from South America as they can be challenging to breed.

They prefer the soft, acidic, slow-moving blackwater of the Negro Rivers. So, you’ll want to do your best to recreate those conditions in your aquarium to keep them happy. 

I recommend getting some experience raising other tetra species before trying Cardinal Tetras due to their specific preferences. 

Cardinal Tetra Appearance and Size

Cardinal Tetras are often mistaken for their close relatives, the Neon Tetra. Cardinals have very bright bodies with electric blue and bright red stripes, much like Neons. However, the lines go the entire way across their bodies, while the red bar stops short on Neon Tetras.

They also have transparent dorsal and anal fins. Their tail fin is mostly clear, too, but the red on their body can spread into their base.

Adult Cardinal Tetras grow to about 1.25 inches (3 cm) and can reach their full size in about a year. They’re pretty small fish, allowing you to keep more in a tank.

Difference Between Males and Females

Male and female Cardinal Tetras look very similar, although the females are much rounder and have larger bellies. The males are straighter and more closely resemble torpedos.

Both males and females are peaceful, although males sometimes show aggressive behavior during mating. This is very rare, so you shouldn’t have to worry much. You can also keep any number of males and females in a school without a problem.

Cardinal Tetra Personality and Behavior

Cardinal Tetras are calm fish that enjoy living in groups. When you consider in the wild they form schools of 100 fish, they can become very stressed if you don’t have enough of them in a tank together.

These tetras are most active during the day and swim energetically through their tanks. You may notice them play chasing with each other when they’re happy. They also love exploring as a school.

You can tell your Cardinals are stressed if they hide constantly, appear to gasp for air, and start losing their brilliant colors. You’ll want to change their tank conditions or increase the size of their school to help them.

Cardinal Tetra Expected Lifespan

In an aquarium, most Cardinal Tetras live for five years. Although they can sometimes live up to ten years in the right conditions.

In the wild, Cardinal Tetras don’t live as long and usually have lifespans of only a year. So by adopting them, you can give them a much happier and longer life.

Cardinal Tetra Care and Tank Set Up

Knowing how to care for your Cardinal Tetra fish will help you keep them happy. You’ll need to keep their water conditions consistent and decorate their tank to match their natural environment.

Tank Size

While you can stock Cardinal Tetras in a 10-gallon tank, you generally want to choose a 20-gallon at least. That way, you have enough room to keep a large school in the aquarium without overcrowding.

A 20-gallon also gives your fish more room to explore and swim. You’ll have enough space to create planted areas for them to hide in and can include open waters for them to zip around.

Plus, if you plan on making a community tank, you’ll have enough room to add other fish species.

How Many Cardinal Tetras Are Suitable for a 20-Gallon Tank?

Up to 10 Cardinal Tetras are suitable for a 20-gallon tank. As a general rule, you want each Cardinal to have two gallons of water. So, you can fit up to 10 in 20 gallons of water. You need at least six Cardinals in a tank.

A 10-gallon tank is enough space for five Cardinal Tetras, but you might push the bio-load a bit by adding another to complete the school. So, I recommend using tanks of at least 20 gallons for this kind of tetra.

Water Parameters

  • Water temperature: 73°F to 81°F (23 to 27°C)
  • Water pH levels: 4.6 to 6.2
  • Water hardness: Under 4 dGH

Cardinal Tetras come from slow-moving, soft, acidic waters that mostly get filtered light. Their tank set-up can be challenging for beginners, it will be easier if you have experience with other tetras. 

Water Temperature

Since they’re tropical fish, these tetras like warmer water and prefer temperatures between 73°F to 81°F (23 to 27°C). You may not need a water heater if you live somewhere warm enough. 

You will want a heater if you can’t keep the water at a consistent temperature. I recommend the FREESEA 75 Watt Water Heater from You can easily set the temperature, and it will keep it at that level. I also appreciated its easy-to-read LED temperature display, so you always know if the tank’s warm enough.

Water pH Levels

Your Cardinal Tetra will need acidic water. Adding driftwood and peat moss to the tank can help lower the pH into this tetra’s preferred range. Many fishkeepers also use carbon dioxide reactors.

Cardinal Tetras can survive in water with a pH between 4.6 to 6.2. They’re tough and can survive outside that range for a while, but it’s best to monitor and adjust the pH when needed.

Water Hardness

You’ll need to keep the water hardness under 4 dGH. Anything harder than that, the tetras will become sick quickly and have a much shorter lifespan. Cardinal Tetras don’t respond very well to minerals in their water.

Peat moss and driftwood can also soften the water. The moss is the better option because it’s much easier to remove after it absorbs minerals.

You can also use water softeners made specifically for tetras. Research the product and follow the directions to prevent harm to your fish.

Water Current

Cardinal Tetras come from rivers with some water current, so they prefer it in their tanks. However, you must ensure the water flow isn’t strong since they’re tiny fish.

The ideal tank set-up for Cardinals features an area of gentle current and one of still water. That way, your fish have somewhere to rest and sleep without being pushed around.

A moderate current will also help to stir more oxygen into the water, which keeps your fish healthy.

What To Put in the Tank

Knowing what to put in your aquarium will help you build the perfect environment for your fish. You’ll want to consider what substrate you’ll use, decorations, and even live plants.


Cardinal Tetras don’t venture to the bottom of the tank often, so you can use various substrates.

Sand is the best option because it would be found in its natural habitat. Very fine sand is also small enough that the fish won’t choke on it if they do happen to explore the bottom of their tank.

Pebbles, rocks, and gravel are fine as long as it’s large enough that your tetras can’t get them into their mouths.

Lastly, dark substrates are better for making your tetra’s bright colors stand out more. They prefer it, too, since they come from dark rivers.


Since Cardinal Tetras are small prey fish, they appreciate having plenty of spaces to hide. You’ll want to offer them caves, plants, and other decorations to swim through.

A great option is to build your own caves. You can place a water-safe pipe in the tank, then cover it with substrate, rocks, and driftwood while leaving it open for the fish to enter. You could even attach live plants to the cave to make it look natural.

Many pet stores have plenty of premade decorations that are perfect for tetras as well.

Ideal Plants

Cardinal Tetras love having floating live plants in their aquarium. This vegetation provides filtered light, which they would experience in the wild.

Java Fern is a great option. It offers a lot of shade and protection and matches Cardinal Tetras’ preferred water parameters. It’s even easy to take care of

Water lettuce is another excellent choice for tetras. The plant floats along the top of the water, creating the filtered light that these fish love.

You can also try Amazon Sword plants. This plant makes an excellent backdrop for tanks, is easy to maintain, and looks great.


Cardinal Tetras live in blackwater rivers, so they like it darker than most other fish. Although, you do need to make sure they get between 12 to 14 hours of light each day. I find it’s easiest to do this with an aquarium light set on a timer.

However, they don’t like direct light. You’ll need to add plants to the tank to help filter out the light. It’s also a good idea to black out the back and sides of the tank to restrict how much light gets inside.


If you keep your house warm, you may not need a water heater for your tetras. However, most people do. 

While these fish can survive between 73°F and 81°F (23 and 27°C), you’ll want to keep it on the warmer side of that range. Many aquarists recommend keeping the water at least 78°F (25.5°C) for Cardinal Tetras.


It’s a good idea to have a filter in your tank. While a single Cardinal Tetra doesn’t make a lot of waste, you need to keep them in large schools. Not having a filter could cause the tank to become dirty very quickly.

Most people prefer to use sponge filters or hang-on filters with tetras. You don’t want anything too powerful since these are very small fish.

Cardinal Tetra Tank Mates

Cardinal Tetras are peaceful and get along with other small fish. Corydoras, shrimp, and guppies are all excellent options.

Many people also keep their Cardinals with Neon Tetras. The two will form schools together and have similar tank parameters and personalities. 

Tank Mates To Avoid

You don’t want to keep them with anything aggressive or large, as these fish will pick on your tetras. Large cichlids, angelfish, and Jack Dempseys are too aggressive and may try to eat your tetras.

Cardinal Tetras are fin nippers, so don’t keep them with fish with flowing tails.

Cardinal Tetra Food and Diet

Cardinal Tetras are omnivores, so they’ll eat just about anything. Some of the best food to include in their diet are freeze-dried bloodworms, fish flakes, and dried brine shrimp.

It’s best to feed your tetras multiple times during the day. Offer them three or four small meals spread out during their waking hours. You need to only give them enough to eat within two to three minutes so it doesn’t dirty their tank.

Breeding Cardinal Tetras

Cardinal Tetras are difficult to breed in tanks, so they’re usually imported from their natural habitats. However, you can still try it at home if you’d like.

You’ll need to set up a separate breeding tank with these water conditions:

  • A pH between 5.0 and 6.0
  • Very soft water of 4 dGH or lower
  • Water temperature of 82ºF (28ºC)
  • Very little light
  • Live plants

Essentially, you must set up the tank to be as close to their wild environment as possible. This can be challenging for beginners.

Cardinal Tetras Common Health Issues

Knowing what health issues your Cardinals can have will help you prevent them. Like many other tetra species, these fish often suffer from ich and Neon Tetra Disease (NDT).


Ich is a widespread health problem for any fish, including tetras. It’s a parasitic infection that can be fatal to Cardinals if you don’t identify and treat it right away.

Ich Symptoms

Your tetras will start rubbing and bumping into objects in their tank. They’ll develop white patches on their fins and body a few days later.

They can also become lethargic and won’t eat as much. If the ich is on their gills, they’ll gasp for air.

Ich Treatment

You can buy ich treatments at just about any pet shop. However, since Cardinals love warm water, you can also raise the temperature of their tank for two weeks to kill the parasites.

86°F (30°C) speeds up the parasite’s life cycle, causing it to die faster. Just make sure you don’t stop early.

Ich Prevention

The best way to prevent the spread of ich is to quarantine any new fish you get in a separate tank.

If your tetras get ich in a community tank, you must isolate them immediately and start treatment.

Neon Tetra Disease (NTD)

NTD is an illness caused by a parasite that affects the muscles within a tetra’s body. It’s fatal to fish and spreads quickly, so you need to remove fish with it from community tanks right away.

NTD Symptoms

Tetras with NTD usually are restless, struggling to swim, and eventually develop a curved spine or lumps. They won’t eat as much and will separate themselves from the rest of the school.

The disease can sometimes lead to other issues, such as bloating or rotting fins.

NTD Treatment

There is currently no cure for NTD, so you must quarantine any fish that show symptoms as soon as possible. 

It’s very contagious among tetras and usually spreads when fish eat the body of an infected fish.

NTD Prevention

The best way to prevent NTD in a community tank is to quarantine all new fish for several weeks before adding them. You’ll also need to remove infected fish right away, so make sure you know what this disease looks like in Cardinals.

Are Cardinal Tetras Right for You?

Cardinal Tetras are fun, peaceful fish that are great for those with previous experience with tetras. I recommend raising some Neon Tetras first, then adding Cardinals to the tank when you’re more comfortable.

Overall, Cardinal Tetras are excellent for most people who love raising tropical fish.

Cardinal Tetra FAQs

Can I Mix Cardinal and Neon Tetra?

You can mix Cardinal and Neon Tetras in the same tank. They require a lot of the same water conditions and get along well, and will even school together.

These tetras look very similar to each other from a distance. So, many people enjoy keeping them together.

Can I Keep Four Cardinal Tetras?

You shouldn’t keep four Cardinal Tetras as that’s not enough to form a school for this species. Always have six or more Cardinals together in a tank. Having too few causes unnecessary stress in these fish.

If your fish are too stressed, they can be infected by parasites and illness easier. So, always make sure to have enough Cardinals together.

Can Neon and Cardinal Tetras Breed Together?

Neon and Cardinal Tetras can breed together. Although, it can be very difficult to get the Cardinals to reproduce. Since these fish already look similar, it can be hard to identify hybrids. So, you shouldn’t give them to pet stores if they cross-breed.

Neons and Cardinals get along very well, so there are instances where they do breed. Although, it doesn’t happen much.

Wrapping Up

In conclusion, Cardinal Tetras are vibrant, peaceful fish that is excellent in various tanks. You can keep Cardinals with other small fish or have a tank with only a Cardinal school.

These fish are beautiful, and you’re sure to love them! Having experience before getting them can help you care for them properly.

I’m Elle, the founder of FishHQ. I created this website to share knowledge, tips, and inspiration for beginner hobbyists to help them create a healthy, happy, and vibrant environment for their fish to thrive. Read more...