i have my tank in the basement and sometime at cold nights the basement goes down to 65degrees. i have brought two 300watt heater that is controlled by a heater controller which you can buy from ebay for...
http://cgi.ebay.com/Aquarium-Heater...emQQptZLH_DefaultDomain_0?hash=item439af1f5ac
or increase the wattage to 400w heaters..
http://cgi.ebay.com/Aquarium-Heater...emQQptZLH_DefaultDomain_0?hash=item439af1f5ac
or increase the wattage to 400w heaters..