Overview
The cardinal tetra is a small blackwater shoaling fish from the upper Rio Negro and Orinoco basins. It looks like a neon tetra turned up to eleven: the electric-blue stripe is paired with a brilliant red band that runs the entire length of the body.
Cardinals prefer warmer, softer, more acidic water than neons and are slightly less tolerant of hard tap water, but in a mature planted tank they are stunning and long-lived shoalers.
| Care level | Beginner-Intermediate |
| Adult size | 1.5-2 in (4-5 cm) |
| Lifespan | 4-6 years |
| Temperament | Peaceful |
| Min. tank | 15 gal (57 L) |
| Temperature | 73-81°F (23-27°C) |
| pH | 5.5-7.0 |
| Hardness | 1-8 dGH |
| Diet | Omnivore |
| Schooling | Yes , keep 6 or more |
Water & tank conditions
Cardinals come from very soft, acidic blackwater. Target pH 5.5-7.0, low hardness and 73-81°F. They colour up best over dark substrate with tannin-stained water and appreciate stable, mature conditions.
Aquascape & setup
Dense planting, driftwood, leaf litter and floating plants recreate their shaded home and bring out the red and blue. Give the shoal open mid-water swimming room framed by planted edges.
Diet & feeding
An omnivore that takes small flakes, micro-pellets and , for best colour and condition , regular frozen or live daphnia, cyclops, baby brine shrimp and crushed bloodworms.
Tankmates & schooling
Keep six or more; larger shoals look spectacular. Pair with other peaceful soft-water community fish (rasboras, pencilfish, corydoras, dwarf cichlids, shrimp). Avoid anything big enough to eat them.
Breeding
Difficult in the home aquarium. Spawning needs extremely soft, acidic, dim water; the eggs are light-sensitive and most farmed cardinals are still wild-caught from the Rio Negro.
Fun facts
- The cardinal's red stripe runs the full body length , the easiest way to tell it from a neon tetra.
- Most cardinal tetras in the trade are sustainably wild-caught, supporting the 'Project Piaba' fishery in Brazil.
- Their colours are richest in soft, dark, tannin-stained blackwater.
- They can live 4-6 years, longer than many people expect from such a small fish.
- Like neons, the blue is a structural, light-reflecting colour.
Frequently asked questions
Are cardinal tetras hard to keep?
They are only slightly more demanding than neon tetras. They prefer soft, warm, acidic water and a mature tank, but in the right community setup they are peaceful and hardy.
How many cardinal tetras should I keep?
Keep at least six; larger shoals of 10-20 look and behave best, staying confident and tightly grouped.
Can cardinal and neon tetras be kept together?
Yes , they are peaceful and occupy the same niche, though they will not school together as one group. Water preferences overlap enough for a shared community tank.
What do cardinal tetras eat?
They are omnivores. Feed small flakes or micro-pellets and supplement with frozen or live daphnia, cyclops and baby brine shrimp for the best colour.
What size tank do cardinal tetras need?
A shoal needs at least 15 gallons (57 litres); larger tanks support the bigger groups they thrive in.
