Interpet Aquatherm Aquarium Heaters are an accurate tool to ensure the correct heating of your tropical fish tank water To ensure a Tropical tank thrives, maintaining the correct temperature is a key component of aquarium care. The Interpet Aquatherm Aquarium Heaters are slim line submersible heaters that are easy to use and control. Each heater has a convenient top located control knob that is easy to turn, and in doing so the value shows up on the glass front to clearly display the desired temperature. The front of each heater has a clear to see On/Off LED light that indicates the heater is working. Each tube is made of high quality glass with safety in mind. It is recommended the heater is attached to the side of the aquarium diagonally, submersed under water. Use the provided suckers to attach to the glass. The maximum operating depth is 1.2m, giving you options where you wish to install.