will the heater harm the fish if it was in the water? i have 3 pockets in my aquarium, 1 for the filter, one for the heater, and 1 i dont know why is it for, why is it for ? so the heater i puted it in the aquarium and i was kinda thinking of getting an extra heater for the heater pocket, like that in case 1 fail, i have a seconde one running, coz the one i currently have isent satisfying me enough, the water temp is 22.C or 23 Csometimes, 24 /25 isent better?