My heater was going up to 80 or 82, but when I unplugged it the temp stayed up there. Turned out it was the motor of the HOB that was doing it. And now everything works fine, since I cleaned out the HOB motor.
I have a 10g that was a generous donation from a friend who's contemplating moving. I bought two 13w bulbs but they were way too much. I have 10ws on now and I'm still having slight algae problems. Java Moss is growing like crazy. Oh, I have a glass cover covered with screen material, as I live in an apartment and can't hang the lights and raise them some above the tank. I really think that either there's not enough of some nutrient or the lights are just too bright.
10 gallon tank; 2x 10W CFL; Fluval U2; MGOCPM/PETCO black sand cap
A Quiet Cycled Tank
The Fraternity of Dirt #152