The wattage of the heater really will not be the problem. You see, you don't wont the water temperature in the aquarium to change up or down more than 1F in a day. So even if it were a 100 watts heater it would still be good. When the temp gets to where you have it set the heater will just cycle off. Some people even use two heaters. What will be a problem is setting the thermostat.
Heat another container of water, with whichever heater you get. Set the thermostat using two thermometers before you put it in your aquarium. When you like the readings you are getting from both thermometers unplug the heater then transfer it to the aquarium.
In all my aquariua I use no less than 5 watts per gallon, but most are 10 watts per gallon. Heat control is one of the 3 reasons not to employ a small aquarium.The best way to control the tempature of small aquaria is to control the tempature of the room where you keep it.
Jeff
