Can harlequin rasboras live with pencilfish?

Verdict
Yes

Yes, harlequin rasboras and pencilfish can live together. Both are fine at 75–80°F. Plan on at least 15 gal.

Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5 PencilfishPencilfish75–82°F · pH 5–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 75–80°Harlequin rasbora 72–80°Pencilfish 75–82°
The green band is the temperature range both can live in.
456789Both: 6–7.5Harlequin rasbora 6–7.5Pencilfish 5–7.5
The green band is the pH both tolerate.

Size to scale

Harlequin rasbora · 2 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

Harlequin rasboraPencilfish
Temperature72–80 °F75–82 °F
pH6–7.55–7.5
Adult size2.0 in2.0 in
Minimum tank10 gal15 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Better tank mates for pencilfish

All pencilfish tank mates

Questions

Can harlequin rasboras live with pencilfish?

Yes, harlequin rasboras and pencilfish can live together. Both are fine at 75–80°F. Plan on at least 15 gal.

What temperature suits both harlequin rasboras and pencilfish?

75–80 °F. Harlequin rasboras need 72–80 °F, pencilfish need 75–82 °F.

What size tank do harlequin rasboras and pencilfish need together?

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