Species · Tetras & rasboras
Cardinal Tetra
Paracheirodon axelrodi
The neon's bolder, redder cousin — a stunning soft-water schooler that's actually a touch hardier than a neon in a warm, mature tank. Keep a real group.
Difficulty: Beginner–IntermediateTropical community tank✓ Fact-checked care guide
Quick facts
| Adult size | ~3.5 cm / 1.4 in |
|---|---|
| Minimum tank | ~40 L / 10 US gal for a shoal — SeriouslyFish recommends a 60 × 30 cm base |
| Temperature | 25–28 °C / 77–82 °F (likes it warm; species range 23–29 °C / 73–84 °F) |
| pH | 4.0–7.5 (soft, acidic to neutral) |
| Hardness | 1–12 dGH (soft water) |
| Filtration & flow | Cycled, gentle filtration; a warm, mature, soft-water tank suits it best |
| Diet | Micro-omnivore — small flake/micro-pellet plus tiny live/frozen foods |
| Social | Shoaling — keep at least 6, more is better |
| Temperament | Very peaceful |
| Lifespan | 4–5 years |
Overview
The cardinal tetra (Paracheirodon axelrodi) is the deeper, fuller-coloured cousin of the neon — its red stripe runs the full length of the body. In a real group it is one of the most beautiful fish in the hobby.
Unlike the neon, a good share of cardinals are still wild-caught (often via sustainable community fisheries like Project Piaba). Given warm, soft, mature water they are hardy and long-lived — and slightly tougher than neons in a warm tank.
Water & tank
Cardinals are a warm, soft-water fish: they do best at 25–28 °C / 77–82 °F in soft, acidic-to-neutral water (pH 4.0–7.5, 1–12 dGH). They colour up beautifully in a planted, gently-lit, tannin-stained tank.
As with neons, add them only to a fully cycled, mature aquarium — never a brand-new one. Give a shoal at least ~40 L / 10 US gal (SeriouslyFish recommends a 60 × 30 cm base).
Feeding
A micro-predator with a tiny mouth — a small-grade flake or micro-pellet base plus tiny live/frozen foods (daphnia, baby brine shrimp) for colour and condition. Feed small amounts once or twice a day.
Behaviour & tankmates
A model peaceful community fish — keep a group of 6+ (more looks far better) with other small, calm species. Avoid fin-nippers and anything big enough to eat them (angelfish included).
What to expect
A settled group schools loosely and glows deep red-and-blue; persistent fading or a fish leaving the group is worth a closer look, starting with a water test.
Myths, kindly busted
“Cardinals and neons are the same fish.”
Similar, but the cardinal is bigger, deeper-coloured (red runs the full body), likes it warmer, and is often wild-caught.
“A few cardinals are enough.”
They are shoaling fish — keep at least 6 (more is better) or they stay stressed and pale.
When to act
We triage, not diagnose — but these are worth a closer look (starting with a water test):
- New fish looking pale or hollow-bellied — confirm the tank is fully cycled and mature; test ammonia/nitrite/nitrate.
- White spots, clamped fins or rapid breathing across the group — test the water and act early.
Sources & further reading
- SeriouslyFish — Paracheirodon axelrodi — Adult ~35 mm SL; recommended 60 × 30 cm base; temperature 23–29 °C / 73–84 °F (warm); pH 4.0–7.5; hardness 1–12 dGH (soft); very peaceful shoaling community fish; often wild-caught (e.g. Project Piaba).
Written & fact-checked by The Finfern Team against the sources above — kind, general guidance, not a diagnosis. If something looks wrong, test your water and, if it persists, contact a fish-savvy vet.
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