Cardinal tetras are the vivid red-and-blue shoaling fish that look almost identical to neon tetras but are hardier, not prone to Neon Tetra Disease, and — with their red stripe running the full body length — arguably more striking. A large shoal in a planted blackwater tank is one of the most beautiful sights in the hobby.

Here is how to keep them.

Quick facts

• Adult size: 3–4 cm
• Tank size: 60 litres for a shoal of 8+
• Water: pH 5.5–7.0, soft, 24–27 °C
• Lifespan: 4–5 years
• Temperament: peaceful, shoaling

Tank setup

Cardinals come from soft, acidic blackwater and colour up best over dark substrate with dense planting and Indian almond leaves that tint the water. In hard-water areas, see how to lower pH. Keep them in a mature, cycled tank.

Shoaling and feeding

Keep a shoal of at least 8, ideally more — cardinals only show natural behaviour and colour in groups. Feed small micro foods and frozen daphnia or brine shrimp.

Tank mates

Good tank mates: other small tetras, corydoras, otocinclus, honey gouramis, cherry shrimp. Avoid angelfish and other fish large enough to eat them.

Frequently asked questions

Are cardinal tetras hardier than neon tetras?

Yes. Cardinal tetras are hardier in transport and are not susceptible to Neon Tetra Disease, making them the better choice despite costing slightly more.

How many cardinal tetras should be kept together?

At least eight, ideally more. They are shoaling fish that show their best colour and natural behaviour only in larger groups.

What water do cardinal tetras need?

Soft, slightly acidic water (pH 5.5–7.0) at 24–27 °C in a mature, well-planted tank. Dark substrate and tannins from almond leaves bring out their colour.

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— Jaqline Smalling, FishForever