Cardinal tetra

Behaviour and habits

The cardinal tetra is a peaceful, glowing shoaler closely related to the neon, but with an unbroken red-and-blue line and a preference for warmer, softer, more acidic water. It schools tightly in mid-water and shows to best effect in a large group against plants, staying vivid when it is at ease and fading when stressed. Like the neon, it feels safe only in numbers, so a group of six or more is essential.

What to feed, and how often

It takes anything small: micro-pellet, crushed flake and small frozen foods such as daphnia and bloodworm. Feed two light meals a day, and make sure the food drifts to the shoal; cardinals are gentle, unhurried feeders that can be out-competed by bolder fish.

Water changes and maintenance

Change about 20–25% weekly in warm, soft, acidic water, matched closely and never cold. It is less forgiving than the neon and needs a mature tank; a cold or large water change on a new setup is a classic cause of losses.

Care and how easy it is

Best in a soft-water, well-planted tank with a group of six or more, and more demanding than many tetras. It rewards stable, warm, acidic conditions with brilliant colour.

Lifespan

With good conditions and steady water quality, this species typically lives around 5 years in a home aquarium; some individuals live longer.

Common health problems

Stress-sensitive; prone to ich and to wasting when the water is wrong.

If it gets sick

Quarantine new arrivals, keep the water warm, soft and stable, and treat ich early while watching the whole group for about a week.