Few fish light up a planted tank like a school of cardinal tetras (Paracheirodon axelrodi). Their neon-blue stripe and full-length red belly glow against green plants and dark wood. They are peaceful, inexpensive and stay small, but they do best in a stable, mature aquarium.
| Adult size | About 1.5–2 inches |
|---|---|
| Group size | 8 or more (bigger schools look and behave better) |
| Minimum tank | 20 gallons for a school |
| Temperature | 76–82°F (they like it warm) |
| pH | 5.5–7.2, soft water preferred |
| Lifespan | Around 5 years with good care |
| Temperament | Peaceful |
Cardinal vs. neon tetra
The quick way to tell them apart: on a cardinal tetra, the red runs the full length of the belly. On a neon tetra, the red only covers the back half. Cardinals grow slightly larger and prefer warmer water, which makes them good companions for discus and rams.
Setting up the tank
- Add them to a cycled, established tank. Cardinals are sensitive to ammonia and big swings in water chemistry. See our guide on how to cycle a new aquarium.
- Give them cover and open space. Plants, driftwood and leaf litter along the sides and back, with an open swimming area in the middle.
- Dim the lights a little. Floating plants or botanicals like catappa leaves make them feel secure and bring out their color.
- Use gentle filtration. A sponge filter or a filter with moderate flow is ideal.
Water and maintenance
In the wild, cardinals live in soft, acidic blackwater. Most store-raised cardinals adapt to a wider range, but stable conditions matter more than hitting an exact number. Change 20–25% of the water weekly with dechlorinated water at the same temperature, and avoid big pH swings.
Feeding
Cardinals have small mouths. Feed a quality micro pellet or crushed flake once or twice a day, as much as they eat in about two minutes. Add frozen or live baby brine shrimp or daphnia a couple of times a week for color and condition.
Good tankmates
- Other small, peaceful schooling fish: rasboras, rummy nose tetras and lemon tetras
- Bottom dwellers like corydoras and otocinclus
- Dwarf cichlids such as rams and Apistogramma
- Discus, in a warm, well-maintained tank
Avoid fish large enough to swallow them (adult angelfish can eat small tetras) and fin-nippers or aggressive cichlids.
Common problems
- Faded color or hiding: usually stress from too few fish, bright bare tanks or poor water quality.
- Losses after adding them: most often a young or unstable tank. Acclimate slowly and add them to a mature setup.
- White spots: ich. Raise the temperature gradually and treat promptly with a product such as Hikari ICH-X.
Frequently asked questions
How many cardinal tetras should I keep together?
At least 8, and more if you have room. In bigger groups they school tighter, show better color and are less stressed.
Can cardinal tetras live with bettas?
Often, yes, in a 20-gallon or larger planted tank, as long as the betta is not aggressive. Watch the first days closely.
Do cardinal tetras breed in home aquariums?
Rarely in community tanks. Breeding needs very soft, acidic water and a separate setup.
Why do cardinals lose color at night?
They pale at night or when the lights first come on. It is normal and the color returns within minutes.
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Questions? Call us at 786-642-3001 or visit the store at 8338 West State Road 84, Davie, FL (Wednesday to Sunday, 12–7 p.m.).