Can rummy nose tetras live with upside down catfish?

Verdict
Yes

Yes. Rummy nose tetras and upside down catfish get along in the same tank. Both are fine at 75–79°F. Plan on at least 30 gal.

Rummy nose tetraRummy nose tetra75–84°F · pH 5.5–7 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: 75–79°Rummy nose tetra 75–84°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7Rummy nose tetra 5.5–7Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Rummy nose tetra · 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

Rummy nose tetraUpside down catfish
Temperature75–84 °F72–79 °F
pH5.5–76–7.5
Adult size2.0 in4.0 in
Minimum tank20 gal30 gal
TemperamentPeacefulPeaceful
Swims atMiddleBottom
GroupGroups of 6+Groups of 3+
DietOmnivoreOmnivore

Better tank mates for rummy nose tetras

All rummy nose tetra tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can rummy nose tetras live with upside down catfish?

Yes. Rummy nose tetras and upside down catfish get along in the same tank. Both are fine at 75–79°F. Plan on at least 30 gal.

What temperature suits both rummy nose tetras and upside down catfish?

75–79 °F. Rummy nose tetras need 75–84 °F, upside down catfish need 72–79 °F.

What size tank do rummy nose tetras and upside down catfish need together?

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