Aqueon heaters are constructed from a thermal shatter-resistant glass making it extremely durable. The dual calibration process ensures accuracy to +/- 1 degrees F. Other features includes automatic shut off & overheat protection, where the unit switches itself off if the heater is not properly submersed, avoiding overheating & damage. Suitable for both fresh & saltwater aquariums. Designed for aquariums from 30 to 55 gallons in size. Backed by a Manafacturer's Lifetime Warranty.