Sukeen Aquarium Heater Auto Thermostat Fish Tank Heater for 3-80 Gallons,Shatter-Proof and Blast-Proof,Adjustable Temperature and Extra Thermometer INTERMITTENT OPERATION MODE: This aquarium heater works in intermittent operation mode, when water temperature reaches to specified temperature value, heater will automatically stop heating, when water temperature is lower than the set temperature, heater will automatically start heating, provide a constant warm environment for your pet fish to stay healthy. HIGH QUALITY AND SAFE: Shatterproof and indestructible Quartz Glass, covered with double sealed case, blast-proof and no electricity leakage, preventing your pets being scalding. SUBMERSIBLE DESIGN USE: The heating rods to be completely immersed in water use, please NOT make it out of water. Not put it in the water if the wire or glass tube damaged, unplug the power supply when cleaning the fish tank or refreshing aquarium water. ADJUSTABLE TEMPERATURE: Setting the temperature by the pink button on the top of the heater, temperature setting range: 68 F - 94 F (20~34C). Please refer to picture 5 for heater size guide and temperature setting. BUY ONE GET ONE IN FREE: The aquarium heater come with an extra thermometer in free, provide an accurate control of the tank temperature for your lovely fish pets.