Can mollies live with killifish?

Verdict
Yes, with care

Yes, with care. Mollies and killifish can share a tank, but watch one thing. Different water: mollies want pH 7.5–8.5, killifish want pH 5.5–7.

MollyMolly72–82°F · pH 7.5–8.5 KillifishKillifish70–77°F · pH 5.5–7

What to watch

What works

Water side by side

55°60°65°70°75°80°85°90°Both: 72–77°Molly 72–82°Killifish 70–77°
The green band is the temperature range both can live in.
456789Molly 7.5–8.5Killifish 5.5–7
No pH suits both. One would live in the wrong water all the time.

Size to scale

Molly · 4 inKillifish · 2.5 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

MollyKillifish
Temperature72–82 °F70–77 °F
pH7.5–8.55.5–7
Adult size4.0 in2.5 in
Minimum tank20 gal10 gal
TemperamentPeacefulPeaceful
Swims atTopTop
GroupGroups of 3+Alone or in pairs
DietOmnivoreCarnivore

Better tank mates for mollies

All molly tank mates

Better tank mates for killifish

All killifish tank mates

Questions

Can mollies live with killifish?

Yes, with care. Mollies and killifish can share a tank, but watch one thing. Different water: mollies want pH 7.5–8.5, killifish want pH 5.5–7.

What temperature suits both mollies and killifish?

72–77 °F. Mollies need 72–82 °F, killifish need 70–77 °F.

What size tank do mollies and killifish need together?

At least 20 gal, set by the molly. Add space for each extra fish.