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Cardinal Tetra (Paracheirodon axelrodi) Care Guide

The Cardinal tetra (Paracheirodon axelrodi) is a brightly colored, active schooling fish that makes the perfect peaceful candidate for a community tank. 

Also sometimes called the Red Neon tetra or the “big brother” of the smaller Neon tetra, the Cardinal tetra sports a brilliant blue neon stripe and scarlet band. Did you know that there’s a gorgeous gold variant too? 

These charming fish can create a sparkling display in a small or large aquarium. Read this care guide to find out all you need to know about the dazzling Cardinal tetra.

Cardinal Tetra – Overview

Scientific Name

Paracheirodon axelrodi

Common Name (species)

Cardinal tetra, Red Neon tetra,

Family

Characidae

Origin

Rio Negro and Orinoco in South America, also parts of Venezuela and Brazil

Diet

Omnivore

Care Level

Moderate

Activity

Active, schooling fish

Lifespan

Annual in the wild, but 2 to 5 years when tank-kept

Temperament

Peaceful

Tank Level

Swims all around the water column, but mainly the central area

Minimum Tank Size

20 gallons

Temperature Range

Tropical 73° to 81° Fahrenheit

Water Hardness

2 – 8 dGH

pH Range

4.5 to 7.0

Filtration/Flow Rate

Prefers a moderate to low flow with extremely good filtration

Water type

Freshwater

Breeding

Egg-layer but difficult to breed in captivity

Compatibility

Peaceful community fish

OK, for Planted Tanks?

Safe with plants

Origins

Schultz first described the Cardinal tetra in 1956. The species is found in South America, specifically the Orinoco and Rio Negro, and they are also native to Brazil and Venezuela.

Most of the Cardinal tetras that you find for sale in fish stores are wild-caught. That’s partly because the fish are not easy to raise in captivity, but also because catching fish for the commercial trade provides employment for people who would otherwise turn to deforestation to make a living.

Interestingly, the Cardinal’s appearance varies, depending on where the fish originates. For example, silver-blonde and gold forms are found in the Rio Negro drainage, and fish from the Orinoco drainage have a blue stripe that’s shorter than that of specimens taken from other areas.

Thanks to plentiful numbers in the wild, Cardinal tetras are not currently listed on the IUCN Red List.

Natural Habitat

amazon river

Cardinal tetras inhabit slow-moving river tributaries in heavily forested areas. The waterways here are surrounded by dense rainforest, where overhanging trees and fallen leaves create a dimly lit blackwater habitat.

Here, the fish live in large schools, feeding on tiny crustaceans, worms, and plant matter.

Appearance

The fish have a bluish body with a bright blue neon stripe that extends from the tetra’s nose down the length of its body. Underneath the neon blue is a broad crimson band.

Cardinal tetras resemble the Neon tetra, although Cardinals are slightly bigger, and the Neon’s red stripe only extends halfway along the body.

Is Your Cardinal Tetra Male or Female?

Both sexes look much the same. However, female Cardinal tetras are usually plumper than males, and male fish tend to be brighter in color.

Other varieties

As mentioned earlier, you can sometimes find a golden variant, which has a pale, silvery blue stripe. 

Size

Cardinal tetras are very small fish, only growing to reach around 2 inches in length, making them ideal fish for life in a small tank.

Life Expectancy

Cardinal tetras live for between 2 to 5 years in captivity, although they are an annual species, typically surviving for just one year in nature.

Activity Level/Temperament

Cardinal Tetras are very active, peaceful fish that are happiest when kept in a large school.

Unfortunately, like many tetra species, the Cardinal can be a fin nipper.

Compatibility and Tankmates

Since Cardinal tetras are schooling fish, I recommend that you have a shoal of half a dozen or more of these beautiful fish. Not only will the fish be happier in a conspecific group, but they will create a more impressive display in the aquarium. So, that’s a win-win for you and your tetras!

Tank Mates

Good tank mates for Cardinal tetras are other small peaceful species such as rasboras, danios, Corydoras catfish, Dwarf gouramis, and Bolivian rams.

Zebra Danio fishes with a blue background.

Invertebrates such as shrimp and snails make suitable companions for Cardinal tetras and can also provide a useful cleanup crew in the tank.

Fish to Avoid

I recommend that large, aggressive species should be avoided, as they might harass or even attempt to eat the Cardinals.

That said, tetras can be a nuisance,too, nipping the fins of fish with flowing tails such as bettas.

Feeding

To keep them healthy, feed your Cardinal tetras a high-quality, varied, nutritious diet. 

I advise against buying cheap food. The price of budget fish food is usually reflected in its heavily-padded content that contains little of nutritional value for your fish and can even be harmful to them.

What to Feed Your Cardinal Tetras

Cardinal tetras are classified as omnivores.

In the wild environment, Cardinal tetras eat insects, worms, and some plant matter. Captive Cardinals are not fussy feeders, and they will accept a diet of tropical fish flakes, pellets, frozen brine shrimp, bloodworms and similar.

Cardinal tetras have very high vitamin requirements, so their diet needs to contain at least 75% high-quality tropical flakes.

Can You Feed Cardinal Tetras Live Foods?

Cardinal tetras love live foods and will be very appreciative of any that you offer them. However, unless you have your own home brine shrimp hatchery, it’s safer not to feed live food to your fish.

How so?

Well, unfortunately, live food tends to come with a few unwanted added extras in the form of bacteria and parasites, which you certainly don’t want in your aquarium. If you do buy live food from a pet store, always remove the food from the water it’s supplied in before feeding your fish.

Similarly, you must never harvest worms and insect larvae from the natural environment. Although that might seem like a good idea, you could accidentally bring parasites into your tank.

The best source of meaty protein for your Cardinals is frozen food. You can buy a wide variety of different frozen critters, all of which your fish will love.

How Much and How Often to Feed

Little girl feeding fishes in the aquarium.

You should feed your Cardinal tetras two or three times every day.

Only offer the fish what they will eat in two to three minutes. 

Don’t overfeed your tetras. Any food that’s left uneaten will end up in the substrate, where it will gradually rot and pollute the water, placing a greater load on your biological filter.

Tank Requirements

Tank size

I recommend a tank size of 20-gallons for a small group of Cardinal tetras. A larger aquarium is better if you have the space for one, as these are lively, active fishes that need plenty of space to swim, especially if you’re planning on keeping a community tank.

Although a long tank offers more swimming space and a greater surface area to allow good gaseous exchange, Cardinals will be just as happy in a tall tank, since they swim in all areas of the water column.

Tetras are very capable jumpers, so you will need a tank with a lid or a cover slide to prevent any accidental escapes.

Tank Setup

Substrate

Cardinal tetras live in a blackwater river environment. So, add a bag of aquarium-safe peat to the filter and scatter some dried leaves on top of the substrate to help create blackwater. 

The best substrate to use is dark river sand, which looks natural and helps to show off the fishes’ bright colors.

Decoration

Your tank decor can continue the natural-looking theme with rocks, twisted roots, water-smoothed stones, and driftwood. Make sure that your aquascape provides lots of open water for swimming and schooling.

There aren’t many plants in the Cardinal’s river home, largely because the lighting is so poor. However, you might want to include some low-light specialist plants for aesthetics and to give the fish a few hiding places to seek out if they want to. Floating plants are ideal for this kind of setup as they help to diffuse the light and provide shelter for the fish.

Habitat Requirements

Neon Cardinal Fish

Cardinal tetras are pretty straightforward to care for but you must provide them with very clean, well-filtered water. Ideally, Cardinal tetras should be added to an established tank rather than a brand-new setup.

Filtration

As mentioned above, Cardinals need very clean water, so you’ll need a high-quality filtration system. The water in which these fish live tends to be slow-moving, so an external  HOB or canister filter system would probably be the best choice.

Water Parameters

Water Temperature

Black Skirt Tetras are tropical fish that need a water temperature of between 73° and 81° F, ideally in the middle of that range.

Water Hardness and pH Range

The water pH needs to be between 4.5 and 7.0, with a water hardness of 2 to 8 dGH.

Lighting

close up image of underwater landscape nature style aquarium tank with a variety of aquatic plants inside.

In the Cardinal’s natural habitat, the water is shaded by the overarching forest canopy. So, you should use subdued lighting in the tank to replicate the tetra’s wild environment.

An LED lighting unit that offers adjustable lighting effects is a good choice, as that enables you to set the light levels to suit your fish and plants, too. 

Tank Maintenance

Pro Tip 

You’ll need to perform 25% to 50% water changes every other week or 30% weekly if the tank is densely stocked.

While you’re changing the water, you need to vacuum the substrate, paying particular attention to areas where waste accumulates such as tank corners, underneath ornaments, and between plant bases.

Keep the viewing panes clear by using an algae magnet to scrub away algae.

Once a month, you need to clean the filter media by rinsing it in dirty aquarium water, and you’ll need to replace spent cartridges and media when required. Check the filter manufacturer’s recommendations for guidance on that.

Setting Up the Aquarium

Gather what you’ll need to set up your new tank, including: 

Asian women set the fish tank
  • Dark river sand
  • LED lighting unit
  • HOB filtration system
  • Water conditioner
  • Heater
  • Aquarium thermometer
  • Driftwood, twisted roots, smooth stones, rockwork
  • Dried leaves
  • Aquarium-safe peat
  • Low-light plants, floating plants

How to Set up Your Aquarium

  1. Rinse any dust from the river sand under running water. 
  2. Place two or three inches of sand into your aquarium. Put an upside-down plate or bowl on top of the sand in the center of the tank. (You’ll see why in a moment!)
  3. Plug in the heater and filter but don’t switch them on yet. 
  4. Add dechlorinated tap water to the tank, pouring the water over the upside down plate or bowl so that the sand isn’t displaced. 
  5. The water needs to contain a small quantity of ammonia to get the nitrogen cycle started. That’s crucial, as you can’t safely add any fish to the tank until the cycle has completed properly. So, either add a few drops of pure ammonia to the water, sprinkle a little fish flake on the water surface, or put a handful of substrate from an existing, cycled tank into the aquarium.
  6. Wash dust from your decor and arrange the items in the aquarium as desired. 
  7. If you’ve decided to include living plants in your aquascape, you’ll need to prepare them by snipping off dead leaves and damaged stems. Add the plants to the setup.
  8. Switch on the aquarium heater and filtration system. Live plants need eight to ten hours of light each day to photosynthesize, so set your lighting unit’s timer to accommodate that.

Now you need to sit back, relax, and wait for the tank to cycle! That can take ten days or longer, depending on how long it takes for nitrifying bacteria to grow in the biological filter media and over the surfaces within the aquarium.

Test the water every day or so until ammonia and nitrite levels are zero and nitrates are ideally under 20ppm. You may need to allow more time for the cycle to complete, so patience is the key here.

Health and Disease

The primary cause of health issues with Cardinal tetras is poor water quality. So, provided you maintain your tank correctly and keep it clean, you shouldn’t have any issues with disease.

Signs of Good Health

Cardinals are active fishes that should school with their tank mates and busily explore their environment.

Red Flags

Here are a few signs to watch out for that might indicate potential health issues for your Cardinals:

  • Not eating
  • Inactivity
  • Not schooling
  • Ulcers, open sores, or red patches on the body
  • Flicking the body against the substrate or decorations

Common Health Issues and Treatment

Health Issue

Ich (White Spot Disease)

Flukes

Fungal infections

Bacterial infections

Symptoms or Causes

Ich is also called White Spot disease and is caused by a parasite. 
Infected fish have a rash of tiny white spots on the body, fins, and gill covers, and typically flick or rub against objects in the tank.

Flukes is an umbrella term that describes several species of external fish parasites. You may see flukes or worms attached to the fish’s body or gills.

White fluffy growths on the fish’s mouth, head and body.

Bloody, ragged fins. Red patches, sores, ulcers on the body.

Suggested Action

Raise the tank temperature to 82o F for three days. Use an OTC  White Spot treatment to dose the tank.

Treat the aquarium with an antiparasitic medication.

Quarantine infected fish. Treat with an OTC fungus medication.

Treat the aquarium with antibacterial treatment.

Health Issue

Ich (White Spot Disease)

Symptoms or Causes

Ich is also called White Spot disease and is caused by a parasite. 
Infected fish have a rash of tiny white spots on the body, fins, and gill covers, and typically flick or rub against objects in the tank.

Suggested Action

Raise the tank temperature to 82o F for three days. Use an OTC  White Spot treatment to dose the tank.

Health Issue

Flukes

Symptoms or Causes

Flukes is an umbrella term that describes several species of external fish parasites. You may see flukes or worms attached to the fish’s body or gills.

Suggested Action

Treat the aquarium with an antiparasitic medication.

Health Issue

Fungal infections

Symptoms or Causes

White fluffy growths on the fish’s mouth, head and body.

Suggested Action

Quarantine infected fish. Treat with an OTC fungus medication.

Health Issue

Bacterial infections

Symptoms or Causes

Bloody, ragged fins. Red patches, sores, ulcers on the body.

Suggested Action

Treat the aquarium with antibacterial treatment.

Breeding

Cardinal tetras are egg-layers. However, because they are tricky to breed in captivity, most of the specimens you see for sale in pet stores are wild-caught.

Availability

You can buy Cardinals at most fish stores for a few dollars each. Usually, you can get a discount price if you buy a group of fish, which makes sense, since these are a schooling species.

Product Recommendations

  • Water conditioner/dechlorinator
  • Algae magnet
  • Aquarium thermometer
  • Aquarium vacuum
  • Books on keeping tropical fish
  • HOB filter
  • Aquarium (minimum size 20 gallons)
  • Heater
  • High-quality tropical fish flakes, mini pellets, frozen foods
  • LED lighting unit
  • Floating and low-light plants
  • Smooth stones, driftwood, twisted roots
  • Dark river sand substrate

In Conclusion

I hope you loved our guide to the bright and beautiful Cardinal tetra.

These dazzling nano fish make a sparkling addition to a peaceful community aquarium and are quite easy to look after, when given the correct water conditions. 

Tell us about your Cardinals in the comments box below!

And, please share this guide if you enjoyed it.

Alison Page has been an avid fish keeper for over 35 years and has owned many different species of freshwater tropical fish including bettas. Currently Alison has two large freshwater tanks. The first tank has two huge fancy goldfish who are almost ten years old and still looking as good as ever. In the other, she has a happy community of tiger barbs, green tiger barbs, corydoras catfish, platys, and mollies.

2 thoughts on “Cardinal Tetra (Paracheirodon axelrodi) Care Guide”

  1. I’ve got a lotto learn. I’ve got sand in my 20 gallon tank with plants, I got the tank already set up and had to replace the water ASAP . I plan on a Community tank with Molly’s, Plattsburgh, Guppies.Not sure howto treat water before adding fish. Also ,Fish didn’t look healthy today. Where is best place to buy healthy fish? Thanks

    Reply
    • Hi Donna

      Welcome to Tankarium!

      It sounds like you need to check out our articles on the Nitrogen Cycle and How to Care For Freshwater Fish.

      Your tank must be fully-cycled before you add any fish, otherwise, they will probably die. Before adding tap water to the tank, you need to treat it with a dechlorinator, and you can read all about that in this article.

      The choice of fish that you want for your community tank sounds fine. Maybe add some corydoras catfish too. They’re super-cute, very hardy, and perfect for a beginner. You can buy healthy fish from most good small fish stores and online too.

      Hope that helps! Enjoy your fish!

      Alison Page
      Site author

      Reply

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