Can severums live with black ghost knives?

Verdict
Yes

Yes. Severums and black ghost knives make a good pair. Both are fine at 74–82°F. Plan on at least 125 gal.

SeverumSeverum74–84°F · pH 6–7 Black ghost knifeBlack ghost knife73–82°F · pH 6–8

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 74–82°Severum 74–84°Black ghost knife 73–82°
The green band is the temperature range both can live in.
456789Both: 6–7Severum 6–7Black ghost knife 6–8
The green band is the pH both tolerate.

Size to scale

Severum · 8 inBlack ghost knife · 15 in0"2"4"6"8"10"12"14"
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

SeverumBlack ghost knife
Temperature74–84 °F73–82 °F
pH6–76–8
Adult size8.0 in15.0 in
Minimum tank55 gal125 gal
TemperamentSemi-aggressiveSemi-aggressive
Swims atMiddleBottom
GroupAlone or in pairsOne per tank
DietOmnivoreCarnivore

Better tank mates for severums

All severum tank mates

Better tank mates for black ghost knives

All black ghost knife tank mates

Questions

Can severums live with black ghost knives?

Yes. Severums and black ghost knives make a good pair. Both are fine at 74–82°F. Plan on at least 125 gal.

What temperature suits both severums and black ghost knives?

74–82 °F. Severums need 74–84 °F, black ghost knives need 73–82 °F.

What size tank do severums and black ghost knives need together?

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