I just bought a heater today because one fish that body grow something on it s body, and looks like white dot. they said I need a heater rising up my temp to kill that little white dot from fish. and I just bought and installed into my tank. when I plug in the light is on, and then 2 mins , the light off, and I wait half hour still off. I heard someone said that the heater will warm up the water slowly? it takes 24 hours to warm to 28 C from 25 C?