Hi Matt, It may not be the heaters, thermostats, or thermometers. It could be that the heaters are not properly sized for your conditions, especially with this very cold weather! How many gallons is the aquarium that you have the two 250 watt heaters in? What temperature are you trying to maintain in the aquarium? What are the maximum and minimum room temperatures where the aquarium is kept? Roy _______________________________________________ GSAS-Member mailing list GSAS-Member@thekrib.com http://lists.thekrib.com/mailman/listinfo/gsas-member