Can cardinal tetras live with harlequin rasboras?

Verdict
Yes

Yes. Cardinal tetras and harlequin rasboras get along in the same tank. Both are fine at 76–80°F. Plan on at least 20 gal.

Cardinal tetraCardinal tetra76–84°F · pH 4.6–7 Harlequin rasboraHarlequin rasbora72–80°F · pH 6–7.5

Why it works

Water side by side

55°60°65°70°75°80°85°90°Both: 76–80°Cardinal tetra 76–84°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6–7Cardinal tetra 4.6–7Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Cardinal tetra · 2 inHarlequin rasbora · 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

Cardinal tetraHarlequin rasbora
Temperature76–84 °F72–80 °F
pH4.6–76–7.5
Adult size2.0 in2.0 in
Minimum tank20 gal10 gal
TemperamentPeacefulPeaceful
Swims atMiddleMiddle
GroupGroups of 6+Groups of 6+
DietOmnivoreOmnivore

Better tank mates for cardinal tetras

All cardinal tetra tank mates

Better tank mates for harlequin rasboras

All harlequin rasbora tank mates

Questions

Can cardinal tetras live with harlequin rasboras?

Yes. Cardinal tetras and harlequin rasboras get along in the same tank. Both are fine at 76–80°F. Plan on at least 20 gal.

What temperature suits both cardinal tetras and harlequin rasboras?

76–80 °F. Cardinal tetras need 76–84 °F, harlequin rasboras need 72–80 °F.

What size tank do cardinal tetras and harlequin rasboras need together?

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