Can rams live with cardinal tetras?

Verdict
Yes

Yes. Rams and cardinal tetras make a good pair. Both are fine at 80–84°F. Plan on at least 20 gal.

German blue ramGerman blue ram80–86°F · pH 5–7 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: 80–84°German blue ram 80–86°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 5–7German blue ram 5–7Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

German blue ram · 2.5 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

German blue ramCardinal tetra
Temperature80–86 °F76–84 °F
pH5–74.6–7
Adult size2.5 in2.0 in
Minimum tank20 gal20 gal
TemperamentPeacefulPeaceful
Swims atBottomMiddle
GroupAlone or in pairsGroups of 6+
DietOmnivoreOmnivore

Better tank mates for rams

All german blue ram tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can rams live with cardinal tetras?

Yes. Rams and cardinal tetras make a good pair. Both are fine at 80–84°F. Plan on at least 20 gal.

What temperature suits both rams and cardinal tetras?

80–84 °F. Rams need 80–86 °F, cardinal tetras need 76–84 °F.

What size tank do rams and cardinal tetras need together?

At least 20 gal, set by the german blue ram. Add space for each extra fish.