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.