Can cardinal tetras live with upside down catfish?

Verdict
Yes

Yes, cardinal tetras and upside down catfish can live together. Both are fine at 76–79°F. Plan on at least 30 gal.

Cardinal tetraCardinal tetra76–84°F · pH 4.6–7 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: 76–79°Cardinal tetra 76–84°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7Cardinal tetra 4.6–7Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Cardinal 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

Cardinal tetraUpside down catfish
Temperature76–84 °F72–79 °F
pH4.6–76–7.5
Adult size2.0 in4.0 in
Minimum tank20 gal30 gal
TemperamentPeacefulPeaceful
Swims atMiddleBottom
GroupGroups of 6+Groups of 3+
DietOmnivoreOmnivore

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can cardinal tetras live with upside down catfish?

Yes, cardinal tetras and upside down catfish can live together. Both are fine at 76–79°F. Plan on at least 30 gal.

What temperature suits both cardinal tetras and upside down catfish?

76–79 °F. Cardinal tetras need 76–84 °F, upside down catfish need 72–79 °F.

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

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