Can rummy nose tetras live with black ghost knives?

Verdict

No. Rummy nose 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 rummy nose tetras do.

Rummy nose tetra75–84°F · pH 5.5–7

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 rummy nose tetras do.
Watch outBlack ghost knives grow to 15 inches and need 125 gallons, far more than a tank set up for rummy nose tetras.

What works

Both are fine at 75–82°F.
pH 6–7 suits both.
They use different parts of the tank: rummy nose 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

	Rummy nose tetra	Black ghost knife
Temperature	75–84 °F	73–82 °F
pH	5.5–7	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 rummy nose tetras

All rummy nose tetra tank mates

Better tank mates for black ghost knives

All black ghost knife tank mates

Questions

Can rummy nose tetras live with black ghost knives?

No. Rummy nose 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 rummy nose tetras do.

What temperature suits both rummy nose tetras and black ghost knives?

75–82 °F. Rummy nose tetras need 75–84 °F, black ghost knives need 73–82 °F.

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

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