Cardinal Tetra Care Guide: The More Brilliant Cousin of the Neon

The Cardinal Tetra (Paracheirodon axelrodi) is often described as the more dramatic cousin of the Neon Tetra — and it earns that reputation. While the Neon's red stripe covers only the back half of the body, the Cardinal's vivid red extends the entire length, paired with an equally intense iridescent blue stripe above. A school of Cardinal Tetras in a blackwater-style planted tank is one of the most spectacular sights in freshwater fishkeeping.

Blackwater Origins

Cardinals are native to the Rio Negro in Brazil — one of the world's great blackwater rivers, where tannins from decaying leaves stain the water dark amber and lower the pH to 4.0–5.5. This blackwater origin means Cardinals are less tolerant of hard, alkaline water than Neon Tetras.

Ideal water parameters:

• Temperature: 23–27°C
• pH: 4.6–6.2 (they are most vibrant in soft, acidic water)
• Water hardness: Very soft (0–6 dGH)

If your tap water is hard and alkaline, consider using RO (reverse osmosis) water remineralised to the correct parameters, or blending it with collected rainwater.

Tank Setup

• Minimum tank size: 60 liters for a school of eight or more
• Lighting: Subdued lighting (use floating plants or leaf litter to diffuse the light) enhances their colour and reduces stress
• Substrate: Dark substrate (black sand or dark gravel) makes Cardinal Tetras look spectacular
• Plants: Java Fern, Anubias, Amazon Swords, and floating plants create a natural blackwater atmosphere

Adding Indian almond leaves or a piece of driftwood releases tannins that naturally soften and acidify the water while creating the tinted water Cardinals love.

Feeding

Like Neon Tetras, Cardinals are micropredators:

• Hikari Micro Pellets: Perfectly sized for Cardinals and nutritionally complete.
• TetraMin Tropical Flakes: A reliable staple flake food.
• Frozen micro foods: Daphnia, baby brine shrimp, and micro worms provide essential protein.

Feed once or twice daily with small portions. Their mouths are tiny — make sure food is appropriately sized.

School Size

Like all tetras, Cardinals are obligate schoolers. Keep at least eight, ideally twelve or more. A large school creates the iconic shimmering ribbon of colour that makes Cardinal Tetras so famous. Single fish or small groups are stressed and prone to disease.

Compatible Tank Mates

Cardinals are peaceful and delicate. Keep them with:

• Other small, peaceful tetras (Rummy Nose Tetras, Ember Tetras)
• Corydoras catfish (especially C. sterbai for the warm water end)
• Dwarf cichlids like German Blue Rams (share the water chemistry preference)
• Discus (the classic pairing — Cardinals thrive at Discus temperatures)
• Apistogramma dwarf cichlids

Avoid large fish or any species with a mouth big enough to swallow a 5 cm fish.