I just had a thought earlier, (could be totally wrong, but I'm "working", so who cares) what if the (2) heaters are working against each other?
In other words, the (1) goes on and the other turns off cuz its warm again (in that small area)
I'd try using one in the display
also, just be patient, I'm guessing you're in High School? if so, you're WAY ahead of the game. people saying "hurry up and get interesting" or that other junk is BS. take your time, or else you'll learn the hard way (dead fish)
slow and steady wins the reef game if you ask me.