MarineLand Precision Heater for Saltwater or Freshwater Aquariums This 150 watt heater is for aquariums up to 40 gallons. Adjustable temperature dial allows you to set the temperature 1 degree with every click. Thermal Switch automatically turns off as temperature rises above an internal preset and turns back on once it cools down. The advanced heating element contains a mica core surrounded by a mesh heating element for superior heat transfer with enhanced durability Advanced mounting bracket securely attaches to glass and provides 3 window positions to view the temperature display Easy to view sliding scale tells the exact temperature setting. Top dial view shows the setting from an additional location.