Can otocinclus live with upside down catfish?

Verdict
Yes

Yes. Otocinclus and upside down catfish make a good pair. Both are fine at 72–79°F. Plan on at least 30 gal.

OtocinclusOtocinclus72–79°F · pH 6–7.5 Upside down catfishUpside down catfish72–79°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°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7.5Otocinclus 6–7.5Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Otocinclus · 2 inUpside down catfish · 4 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

OtocinclusUpside down catfish
Temperature72–79 °F72–79 °F
pH6–7.56–7.5
Adult size2.0 in4.0 in
Minimum tank20 gal30 gal
TemperamentPeacefulPeaceful
Swims atBottomBottom
GroupGroups of 6+Groups of 3+
DietHerbivoreOmnivore

Better tank mates for otocinclus

All otocinclus tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can otocinclus live with upside down catfish?

Yes. Otocinclus and upside down catfish make a good pair. Both are fine at 72–79°F. Plan on at least 30 gal.

What temperature suits both otocinclus and upside down catfish?

72–79 °F. Otocinclus need 72–79 °F, upside down catfish need 72–79 °F.

What size tank do otocinclus and upside down catfish need together?

At least 30 gal, set by the upside down catfish. Add space for each extra fish.