Can discus live with cardinal tetras?

Verdict
Yes

Yes, discus and cardinal tetras can live together. Both are fine at 82–84°F. Plan on at least 55 gal.

DiscusDiscus82–88°F · pH 5.5–7 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: 82–84°Discus 82–88°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 5.5–7Discus 5.5–7Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Discus · 6 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

DiscusCardinal tetra
Temperature82–88 °F76–84 °F
pH5.5–74.6–7
Adult size6.0 in2.0 in
Minimum tank55 gal20 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 5+Groups of 6+
DietCarnivoreOmnivore

Better tank mates for discus

All discus tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can discus live with cardinal tetras?

Yes, discus and cardinal tetras can live together. Both are fine at 82–84°F. Plan on at least 55 gal.

What temperature suits both discus and cardinal tetras?

82–84 °F. Discus need 82–88 °F, cardinal tetras need 76–84 °F.

What size tank do discus and cardinal tetras need together?

At least 55 gal, set by the discus. Add space for each extra fish.