Angelfish with cardinals

Save the Little Fish demo · Large, 55–75 gal · calm, like a pond or swamp · running 621 days · shared October 2026

A beautiful blackwater tank and a very common mistake: grown angelfish hunt small tetras.

Needs changes

The fish

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Cichlids · PterophyllumLC

Predator. Eats any fish that fits in its mouth.

Pterophyllum scalare

Flooded forests of the Amazon basin · flooded forest

Predator. Eats any fish that fits in its mouth.

Long fins. Fin nippers will pick on it.

Photo: Rjcastillo, CC BY 4.0

× 3

Peaceful with each other, but the cardinal school keeps shrinking.

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Tetras · ParacheirodonStaple

Paracheirodon axelrodi

Rio Negro and upper Orinoco, Brazil and Venezuela · blackwater stream

Photo: Paolo Neo, Public domain

× 20

Shared range 24–29°C
Every species is comfortable in this range.
No hybrid risk
No two species here can cross, so any fry that turn up are pure.
Angelfish needs a group of 5+
Angelfish feel safe in groups of 5 or more; you have 3. Small groups hide, lose colour and get picked on.
Angelfish will eat Cardinal tetra
An adult angelfish reaches 15 cm and eats any fish that fits in its mouth, even ones it grew up with.
Stocking 63% of capacity
A rough estimate based on adult body size and tank volume.
Nothing on the bottom
A few bottom fish, such as corydoras, use the floor and eat food that sinks past the others.
Tank size is a guess
Size and stocking checks use a typical tank of the size you picked. Add the real length and volume for a sharper answer.
Some values are estimates
Care data for Angelfish, Cardinal tetra is estimated or taken from the genus, not yet checked against a source.