Can rosy barbs live with pencilfish?

Verdict
Yes

Yes. Rosy barbs and pencilfish get along in the same tank. Both are fine at 75–77°F. Plan on at least 30 gal.

Rosy barbRosy barb64–77°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: 75–77°Rosy barb 64–77°Pencilfish 75–82°
The green band is the temperature range both can live in.
456789Both: 6–7.5Rosy barb 6–7.5Pencilfish 5–7.5
The green band is the pH both tolerate.

Size to scale

Rosy barb · 4 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

Rosy barbPencilfish
Temperature64–77 °F75–82 °F
pH6–7.55–7.5
Adult size4.0 in2.0 in
Minimum tank30 gal15 gal
TemperamentSemi-aggressivePeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for rosy barbs

All rosy barb tank mates

Better tank mates for pencilfish

All pencilfish tank mates

Questions

Can rosy barbs live with pencilfish?

Yes. Rosy barbs and pencilfish get along in the same tank. Both are fine at 75–77°F. Plan on at least 30 gal.

What temperature suits both rosy barbs and pencilfish?

75–77 °F. Rosy barbs need 64–77 °F, pencilfish need 75–82 °F.

What size tank do rosy barbs and pencilfish need together?

At least 30 gal, set by the rosy barb. Add space for each extra fish.