I recently bought a small heater for my small hex aquarium. It's 3-4 gallons max if I can remember ==" Anyways, the tank doesn't seem to be warm as the heater that's 50W. The small heater is 25W; on th ebox it says, it can heat, 10-25 Litres which in US Gallons is 3.33-8.33 Gallons. Yet the hex tank is only 9 litres, approx. 4 gallons. Is this the heater's fault? 
