Posted: Sun Oct 22, 2006 4:30 pm
What sort of light have you got on the tank, and what size is it? If it's a smaller tank, and the light gives off a significant amount of heat, then the water will heat up...
Or you have endothermic guppies xD
That would be cool! You could just get a few of those, throw them in your tank, and you'd never need a water heater!

Ralpheal, "The 'L' is silent."
Frankie, "Young at heart."