Can rummy nose tetras live with cardinal tetras?

Verdict
Yes

Yes, rummy nose tetras and cardinal tetras can live together. Both are fine at 76–84°F. Plan on at least 20 gal.

Rummy nose tetraRummy nose tetra75–84°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: 76–84°Rummy nose tetra 75–84°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 5.5–7Rummy nose tetra 5.5–7Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Rummy nose tetra · 2 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

Rummy nose tetraCardinal tetra
Temperature75–84 °F76–84 °F
pH5.5–74.6–7
Adult size2.0 in2.0 in
Minimum tank20 gal20 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for rummy nose tetras

All rummy nose tetra tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can rummy nose tetras live with cardinal tetras?

Yes, rummy nose tetras and cardinal tetras can live together. Both are fine at 76–84°F. Plan on at least 20 gal.

What temperature suits both rummy nose tetras and cardinal tetras?

76–84 °F. Rummy nose tetras need 75–84 °F, cardinal tetras need 76–84 °F.

What size tank do rummy nose tetras and cardinal tetras need together?

At least 20 gal, set by the rummy nose tetra. Add space for each extra fish.