Can otocinclus live with harlequin rasboras?

Verdict
Yes

Yes. Otocinclus and harlequin rasboras get along in the same tank. Both are fine at 72–79°F. Plan on at least 20 gal.

OtocinclusOtocinclus72–79°F · pH 6–7.5 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: 72–79°Otocinclus 72–79°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6–7.5Otocinclus 6–7.5Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Otocinclus · 2 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

OtocinclusHarlequin rasbora
Temperature72–79 °F72–80 °F
pH6–7.56–7.5
Adult size2.0 in2.0 in
Minimum tank20 gal10 gal
TemperamentPeacefulPeaceful
Swims atBottomMiddle
GroupGroups of 6+Groups of 6+
DietHerbivoreOmnivore

Better tank mates for otocinclus

All otocinclus tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can otocinclus live with harlequin rasboras?

Yes. Otocinclus and harlequin rasboras get along in the same tank. Both are fine at 72–79°F. Plan on at least 20 gal.

What temperature suits both otocinclus and harlequin rasboras?

72–79 °F. Otocinclus need 72–79 °F, harlequin rasboras need 72–80 °F.

What size tank do otocinclus and harlequin rasboras need together?

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