TankmateChecker

Can koi live with killifish?

Verdict

Yes, with care

Yes, with care. Koi and killifish can share a tank, but watch one thing. Water chemistry is a squeeze. The only pH that suits both is around 7.

Koi

Koi59–77°F · pH 7–8.5

Killifish

Killifish70–77°F · pH 5.5–7

What to watch

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 killifish. Fast, alert fish usually stay out of reach.

What works

Both are fine at 70–77°F.

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	Killifish
Temperature	59–77 °F	70–77 °F
pH	7–8.5	5.5–7
Adult size	24.0 in	2.5 in
Minimum tank	Pond	10 gal
Temperament	Peaceful	Peaceful
Swims at	All levels	Top
Group	Groups of 3+	Alone or in pairs
Diet	Omnivore	Carnivore

Better tank mates for koi

All koi tank mates

Better tank mates for killifish

All killifish tank mates

Questions

Can koi live with killifish?

Yes, with care. Koi and killifish can share a tank, but watch one thing. Water chemistry is a squeeze. The only pH that suits both is around 7.

What temperature suits both koi and killifish?

70–77 °F. Koi need 59–77 °F, killifish need 70–77 °F.

What size tank do koi and killifish need together?

A pond. Koi outgrow indoor tanks.