Can otocinclus live with cardinal tetras?

Verdict
Yes

Yes. Otocinclus and cardinal tetras get along in the same tank. Both are fine at 76–79°F. Plan on at least 20 gal.

OtocinclusOtocinclus72–79°F · pH 6–7.5 Cardinal tetraCardinal tetra76–84°F · pH 4.6–7

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–79°Otocinclus 72–79°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 6–7Otocinclus 6–7.5Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Otocinclus · 2 inCardinal tetra · 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

OtocinclusCardinal tetra
Temperature72–79 °F76–84 °F
pH6–7.54.6–7
Adult size2.0 in2.0 in
Minimum tank20 gal20 gal
TemperamentPeacefulPeaceful
Swims atBottomMiddle
GroupGroups of 6+Groups of 6+
DietHerbivoreOmnivore

Better tank mates for otocinclus

All otocinclus tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can otocinclus live with cardinal tetras?

Yes. Otocinclus and cardinal tetras get along in the same tank. Both are fine at 76–79°F. Plan on at least 20 gal.

What temperature suits both otocinclus and cardinal tetras?

76–79 °F. Otocinclus need 72–79 °F, cardinal tetras need 76–84 °F.

What size tank do otocinclus and cardinal tetras need together?

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