Can killifish live with harlequin rasboras?

Verdict
Yes

Yes. Killifish and harlequin rasboras make a good pair. Both are fine at 72–77°F. Plan on at least 10 gal.

KillifishKillifish70–77°F · pH 5.5–7 Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 72–77°Killifish 70–77°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6–7Killifish 5.5–7Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Killifish · 2.5 inHarlequin rasbora · 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

KillifishHarlequin rasbora
Temperature70–77 °F72–80 °F
pH5.5–76–7.5
Adult size2.5 in2.0 in
Minimum tank10 gal10 gal
TemperamentPeacefulPeaceful
Swims atTopMiddle
GroupAlone or in pairsGroups of 6+
DietCarnivoreOmnivore

Better tank mates for killifish

All killifish tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can killifish live with harlequin rasboras?

Yes. Killifish and harlequin rasboras make a good pair. Both are fine at 72–77°F. Plan on at least 10 gal.

What temperature suits both killifish and harlequin rasboras?

72–77 °F. Killifish need 70–77 °F, harlequin rasboras need 72–80 °F.

What size tank do killifish and harlequin rasboras need together?

At least 10 gal, set by the killifish. Add space for each extra fish.