Can silver dollars live with upside down catfish?

Verdict
Yes

Yes. Silver dollars and upside down catfish make a good pair. Both are fine at 75–79°F. Plan on at least 75 gal.

Silver dollarSilver dollar75–82°F · pH 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°Silver dollar 75–82°Upside down catfish 72–79°
The green band is the temperature range both can live in.
456789Both: 6–7Silver dollar 5–7Upside down catfish 6–7.5
The green band is the pH both tolerate.

Size to scale

Silver dollar · 6 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

Silver dollarUpside down catfish
Temperature75–82 °F72–79 °F
pH5–76–7.5
Adult size6.0 in4.0 in
Minimum tank75 gal30 gal
TemperamentPeacefulPeaceful
Swims atMiddleBottom
GroupGroups of 5+Groups of 3+
DietHerbivoreOmnivore

Better tank mates for silver dollars

All silver dollar tank mates

Better tank mates for upside down catfish

All upside down catfish tank mates

Questions

Can silver dollars live with upside down catfish?

Yes. Silver dollars and upside down catfish make a good pair. Both are fine at 75–79°F. Plan on at least 75 gal.

What temperature suits both silver dollars and upside down catfish?

75–79 °F. Silver dollars need 75–82 °F, upside down catfish need 72–79 °F.

What size tank do silver dollars and upside down catfish need together?

At least 75 gal, set by the silver dollar. Add space for each extra fish.