Can red tail sharks live with harlequin rasboras?

Verdict
Yes

Yes. Red tail sharks and harlequin rasboras make a good pair. Both are fine at 72–79°F. Plan on at least 55 gal.

Red tail sharkRed tail shark72–79°F · pH 6.5–7.5 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: 72–79°Red tail shark 72–79°Harlequin rasbora 72–80°
The green band is the temperature range both can live in.
456789Both: 6.5–7.5Red tail shark 6.5–7.5Harlequin rasbora 6–7.5
The green band is the pH both tolerate.

Size to scale

Red tail shark · 5 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

Red tail sharkHarlequin rasbora
Temperature72–79 °F72–80 °F
pH6.5–7.56–7.5
Adult size5.0 in2.0 in
Minimum tank55 gal10 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 harlequin rasboras

All harlequin rasbora tank mates

Questions

Can red tail sharks live with harlequin rasboras?

Yes. Red tail sharks and harlequin rasboras make a good pair. Both are fine at 72–79°F. Plan on at least 55 gal.

What temperature suits both red tail sharks and harlequin rasboras?

72–79 °F. Red tail sharks need 72–79 °F, harlequin rasboras need 72–80 °F.

What size tank do red tail sharks and harlequin rasboras need together?

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