So I was just thinking, would a fish tank heater that is keeping watching at a certain temp(26C for example) COOL the water if the room temperature was 30C?
Don't think so. If the water is above 26C, the fish tank heater that you have set to 26C just shuts off. ^_^
It is a heater. That is what they do. They don't cool things off that are warmer than the setting.