Can koi live with cardinal tetras?

Verdict

No. Koi and cardinal tetras should not share a tank. Koi are coldwater animals (59–77°F); cardinal tetras need 76–84°F. They overlap only at 76–77°F, the edge of both ranges.

Koi59–77°F · pH 7–8.5

Cardinal tetra76–84°F · pH 4.6–7

What to watch

Deal breakerKoi are coldwater animals (59–77°F); cardinal tetras need 76–84°F. They overlap only at 76–77°F, the edge of both ranges.
Watch outWater chemistry is a squeeze. The only pH that suits both is around 7.
Watch outAt 24 inches a koi can swallow a small cardinal tetra. Fast, alert fish usually stay out of reach.

Water side by side

The green band is the temperature range both can live in.

The green band is the pH both tolerate.

Size to scale

Adult length in an aquarium. A fish can swallow anything that fits in its mouth, roughly a third to half its own length for predators.

Care at a glance

	Koi	Cardinal tetra
Temperature	59–77 °F	76–84 °F
pH	7–8.5	4.6–7
Adult size	24.0 in	2.0 in
Minimum tank	Pond	20 gal
Temperament	Peaceful	Peaceful
Swims at	All levels	Middle
Group	Groups of 3+	Groups of 6+
Diet	Omnivore	Omnivore

Better tank mates for koi

All koi tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can koi live with cardinal tetras?

No. Koi and cardinal tetras should not share a tank. Koi are coldwater animals (59–77°F); cardinal tetras need 76–84°F. They overlap only at 76–77°F, the edge of both ranges.

What temperature suits both koi and cardinal tetras?

76–77 °F. Koi need 59–77 °F, cardinal tetras need 76–84 °F.

What size tank do koi and cardinal tetras need together?

A pond. Koi outgrow indoor tanks.