I seem to have constant problem with too much heat in my 720 Litre tank, it is always at about 27c. I also run 2 x 75 watt heating cables (please don't go there), and 300 watt heater which are all controlled via Dennerle temperature controller, and 8 x 39 watt T5's on for about 7 hours. So i did a little experiment and disconnected all the heaters, but obviously left the lights on, and there was no real change. Later i did a large water change and removed the tank heater from the tank. The heating cables were disconnected. So the temperature started at 23c, then by the next day, the temperature rose to 27c, where it remains. Does anyone else have a similiar problem? Well at least i don't need a heater for the time being.