Can otocinclus live with pencilfish?

Verdict
Yes

Yes. Otocinclus and pencilfish make a good pair. Both are fine at 75–79°F. Plan on at least 20 gal.

OtocinclusOtocinclus72–79°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: 75–79°Otocinclus 72–79°Pencilfish 75–82°
The green band is the temperature range both can live in.
456789Both: 6–7.5Otocinclus 6–7.5Pencilfish 5–7.5
The green band is the pH both tolerate.

Size to scale

Otocinclus · 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

OtocinclusPencilfish
Temperature72–79 °F75–82 °F
pH6–7.55–7.5
Adult size2.0 in2.0 in
Minimum tank20 gal15 gal
TemperamentPeacefulPeaceful
Swims atBottomMiddle
GroupGroups of 6+Groups of 6+
DietHerbivoreOmnivore

Better tank mates for otocinclus

All otocinclus tank mates

Better tank mates for pencilfish

All pencilfish tank mates

Questions

Can otocinclus live with pencilfish?

Yes. Otocinclus and pencilfish make a good pair. Both are fine at 75–79°F. Plan on at least 20 gal.

What temperature suits both otocinclus and pencilfish?

75–79 °F. Otocinclus need 72–79 °F, pencilfish need 75–82 °F.

What size tank do otocinclus and pencilfish need together?

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