Can red tail sharks live with cardinal tetras?

Verdict
Yes

Yes. Red tail sharks and cardinal tetras get along in the same tank. Both are fine at 76–79°F. Plan on at least 55 gal.

Red tail sharkRed tail shark72–79°F · pH 6.5–7.5 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: 76–79°Red tail shark 72–79°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 6.5–7Red tail shark 6.5–7.5Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Red tail shark · 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

Red tail sharkCardinal tetra
Temperature72–79 °F76–84 °F
pH6.5–7.54.6–7
Adult size5.0 in2.0 in
Minimum tank55 gal20 gal
TemperamentSemi-aggressivePeaceful
Swims atBottomMiddle
GroupOne per tankGroups of 6+
DietOmnivoreOmnivore

Better tank mates for red tail sharks

All red tail shark tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can red tail sharks live with cardinal tetras?

Yes. Red tail sharks and cardinal tetras get along in the same tank. Both are fine at 76–79°F. Plan on at least 55 gal.

What temperature suits both red tail sharks and cardinal tetras?

76–79 °F. Red tail sharks need 72–79 °F, cardinal tetras need 76–84 °F.

What size tank do red tail sharks and cardinal tetras need together?

At least 55 gal, set by the red tail shark. Add space for each extra fish.