Can cardinal tetras live with firemouth cichlids?

Verdict
Yes

Yes. Cardinal tetras and firemouth cichlids get along in the same tank. Both are fine at 76–84°F. Plan on at least 30 gal.

Cardinal tetraCardinal tetra76–84°F · pH 4.6–7 Firemouth cichlidFiremouth cichlid75–86°F · pH 6.5–8

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–84°Cardinal tetra 76–84°Firemouth cichlid 75–86°
The green band is the temperature range both can live in.
456789Both: 6.5–7Cardinal tetra 4.6–7Firemouth cichlid 6.5–8
The green band is the pH both tolerate.

Size to scale

Cardinal tetra · 2 inFiremouth cichlid · 6 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 tetraFiremouth cichlid
Temperature76–84 °F75–86 °F
pH4.6–76.5–8
Adult size2.0 in6.0 in
Minimum tank20 gal30 gal
TemperamentPeacefulSemi-aggressive
Swims atMiddleBottom
GroupGroups of 6+Alone or in pairs
DietOmnivoreOmnivore

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Better tank mates for firemouth cichlids

All firemouth cichlid tank mates

Questions

Can cardinal tetras live with firemouth cichlids?

Yes. Cardinal tetras and firemouth cichlids get along in the same tank. Both are fine at 76–84°F. Plan on at least 30 gal.

What temperature suits both cardinal tetras and firemouth cichlids?

76–84 °F. Cardinal tetras need 76–84 °F, firemouth cichlids need 75–86 °F.

What size tank do cardinal tetras and firemouth cichlids need together?

At least 30 gal, set by the firemouth cichlid. Add space for each extra fish.