Just buy a heater or add hot water when doing water changes.
Agreed. Large temp changes will severely stress fish if not kill them.:headshake2: Don't add hot water directly to a tank, ever. Good way to kill fish. Temps have to be raised slowly, no more then 1 degree per hour.
I'd keep white cloud mountain minnows, bitterlings and hillstream loaches in a tank located in an air-conditioned room.