Can killifish live with pencilfish?

Verdict
Yes

Yes. Killifish and pencilfish get along in the same tank. Both are fine at 75–77°F. Plan on at least 15 gal.

KillifishKillifish70–77°F · pH 5.5–7 PencilfishPencilfish75–82°F · pH 5–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 75–77°Killifish 70–77°Pencilfish 75–82°
The green band is the temperature range both can live in.
456789Both: 5.5–7Killifish 5.5–7Pencilfish 5–7.5
The green band is the pH both tolerate.

Size to scale

Killifish · 2.5 inPencilfish · 2 in0"1"2"3"4"5"6"
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

KillifishPencilfish
Temperature70–77 °F75–82 °F
pH5.5–75–7.5
Adult size2.5 in2.0 in
Minimum tank10 gal15 gal
TemperamentPeacefulPeaceful
Swims atTopMiddle
GroupAlone or in pairsGroups of 6+
DietCarnivoreOmnivore

Better tank mates for killifish

All killifish tank mates

Better tank mates for pencilfish

All pencilfish tank mates

Questions

Can killifish live with pencilfish?

Yes. Killifish and pencilfish get along in the same tank. Both are fine at 75–77°F. Plan on at least 15 gal.

What temperature suits both killifish and pencilfish?

75–77 °F. Killifish need 70–77 °F, pencilfish need 75–82 °F.

What size tank do killifish and pencilfish need together?

At least 15 gal, set by the pencilfish. Add space for each extra fish.