Can rainbow sharks live with cardinal tetras?

Verdict
Yes

Yes. Rainbow sharks and cardinal tetras make a good pair. Both are fine at 76–80°F. Plan on at least 55 gal.

Rainbow sharkRainbow shark72–80°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: 76–80°Rainbow shark 72–80°Cardinal tetra 76–84°
The green band is the temperature range both can live in.
456789Both: 6.5–7Rainbow shark 6.5–7.5Cardinal tetra 4.6–7
The green band is the pH both tolerate.

Size to scale

Rainbow shark · 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

Rainbow sharkCardinal tetra
Temperature72–80 °F76–84 °F
pH6.5–7.54.6–7
Adult size6.0 in2.0 in
Minimum tank55 gal20 gal
TemperamentSemi-aggressivePeaceful
Swims atBottomMiddle
GroupOne per tankGroups of 6+
DietOmnivoreOmnivore

Better tank mates for rainbow sharks

All rainbow shark tank mates

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Questions

Can rainbow sharks live with cardinal tetras?

Yes. Rainbow sharks and cardinal tetras make a good pair. Both are fine at 76–80°F. Plan on at least 55 gal.

What temperature suits both rainbow sharks and cardinal tetras?

76–80 °F. Rainbow sharks need 72–80 °F, cardinal tetras need 76–84 °F.

What size tank do rainbow sharks and cardinal tetras need together?

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