Can cardinal tetras live with black ghost knives?

Verdict

No. Cardinal tetras and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 2 inches cardinal tetras do.

Cardinal tetra76–84°F · pH 4.6–7

Black ghost knife73–82°F · pH 6–8

What to watch

Deal breakerAn adult black ghost knife eats fish that fit in its mouth, and at 2 inches cardinal tetras do.
Watch outBlack ghost knives grow to 15 inches and need 125 gallons, far more than a tank set up for cardinal tetras.

What works

Both are fine at 76–82°F.
pH 6–7 suits both.
They use different parts of the tank: cardinal tetras the mid, black ghost knives the bottom.

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

	Cardinal tetra	Black ghost knife
Temperature	76–84 °F	73–82 °F
pH	4.6–7	6–8
Adult size	2.0 in	15.0 in
Minimum tank	20 gal	125 gal
Temperament	Peaceful	Semi-aggressive
Swims at	Middle	Bottom
Group	Groups of 6+	One per tank
Diet	Omnivore	Carnivore

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Better tank mates for black ghost knives

All black ghost knife tank mates

Questions

Can cardinal tetras live with black ghost knives?

No. Cardinal tetras and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 2 inches cardinal tetras do.

What temperature suits both cardinal tetras and black ghost knives?

76–82 °F. Cardinal tetras need 76–84 °F, black ghost knives need 73–82 °F.

What size tank do cardinal tetras and black ghost knives need together?

At least 125 gal, set by the black ghost knife. Add space for each extra fish.