External Controller: Our fish tank heater is adjusted by an external controller, which you can mount on the outside edge of the tank. It’s convenient and safe to adjust temperature, no need to take the heater out from water and no risk of burning yourself. Dual Temp Displays: With dual accurate LED digital temp displays, you can read & set the water temp at the same time. It is very easy and convenient for you to recognize and observe the temp change in real time even in the night! Smart Heating: With the built-in temperature sensor and constant temperature heating system, this fish heater will start to work when the water temp is lower than set temp(red indicator), and stop work until the water temp reaches set temp(blue indicator). It can always provide adequate and steady water temperature for your beloved fish.