Cardinal Tetra
Paracheirodon axelrodi
Min Tank Size
60L
Adult Size
5 cm
Lifespan
4 years
School Size
6+
About
Cardinals come from the soft, blackwater rivers of the Orinoco and Negro basins in South America, and they carry that environment's influence in everything about them. The electric blue stripe running along the lateral line pairs with a red band that covers the entire lower body, not just the back half like on a neon tetra. Under proper lighting in a well-planted tank, a school of cardinals is genuinely one of the most striking sights in the freshwater hobby.
They're a bit more demanding than their neon cousins. Soft, acidic water isn't just preferred, it's where they genuinely thrive long-term. pH between 5.0 and 6.8 is the sweet spot, and hardness should stay low. Warmer temperatures suit them well too, around 25 to 28 degrees. In hard, alkaline tap water they survive but rarely reach their full potential, and disease resistance drops noticeably. A blackwater setup with botanicals, peat filtration, or RO-blended water makes a real difference.
Diet is easy to manage. They accept quality flake and micro pellets without fuss, and frozen foods like daphnia, baby brine shrimp, and bloodworms bring out the best color. Feed small amounts twice daily.
In terms of temperament, you won't find a more peaceful fish. They focus almost entirely on schooling and exploring, posing no threat to other species. A group of at least eight looks dramatically better than a group of six, and larger schools produce the signature synchronized movement people keep this fish for.
Browse actual tank builds featuring cardinal tetras and you'll see just how transformative they are in a well-designed aquascape.
Water Parameters
Temperature
°CpH
GH
dGHKH
dKHSwimming Level
Flow Preference
Keeping multiple Cardinal Tetra together
Cardinal Tetra are shoaling fish and need company of their own kind. Keep a group of at least 6. Smaller groups leave them stressed, washed-out in color, and prone to hiding.
Compatibility
Cardinals pair beautifully with other soft, acidic water species. Dwarf cichlids like apistogrammas and rams are classic companions, as are other small tetras, pencilfish, and hatchetfish. Corydoras and small plecos work well on the bottom. Avoid anything large enough to eat them, which includes angelfish once they mature, despite how commonly that combo is suggested. Discus are often kept with cardinals since both share similar water requirements, and it works well if the tank is large enough. Large barbs or anything nippy should be skipped entirely. Dwarf shrimp can coexist but fry are at risk.
Commonly kept with
Species this one is most often paired withCommonly tried but avoid
Often paired, but shouldn't beCare Notes
The most common mistake is adding cardinals to a new or unstable tank. They're genuinely sensitive to ammonia, nitrite, and sudden parameter shifts, and they'll show it quickly. Get the tank fully cycled and stable before they go in. Wild-caught fish, which are still common in the trade, need especially careful acclimation. Drip acclimation over at least an hour is worth doing. Tap water with high GH and KH is the other common failure point. If your water is hard, invest in RO or use a peat-based approach before expecting long-term success with this species.
Behavior & Aggression
Cardinals are completely non-aggressive. There's no fin nipping, no territory defense, and no meaningful hierarchy within the school that causes problems. The only situation where stress-related issues arise is when the school is too small, which causes skittish behavior and fish hugging the bottom or hiding constantly. Keep at least six, ideally more, and they'll be relaxed and active. Aggression toward this species from tankmates is the real concern, not aggression from them.
Things to Know
- Very sensitive to water quality, don't add to uncycled or new tanks
- Wild-caught specimens are more delicate than tank-raised
- May eat dwarf shrimp fry, though adults are usually ignored
- More sensitive than Neon Tetras, especially when newly acquired.
- Requires soft, acidic water (low pH/GH) to thrive.
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