Tetra Submersible Heater is designed to keep your aquatic fish comfortable, with an electronic thermostat that automatically maintains a consistent water temperature of 78 degrees and prevents overheating, extending heater life. An indicator light lets you know when the water is heating (red light) and when it reaches the proper temperature (green light). Inside, silicon carbide crystals improve heat distribution and transfer. The strong glass tube is heat and shock resistant. This submersible heater is easy to use - just attach to the inside of the aquarium wall using the suction cup (included) in an area with good water circulation.Features:AQUARIUM HEATER: Submersible heater is designed to keep your aquarium at the optimum temperature.AUTOMATIC THERMOSTAT: Electronic thermostat keeps water at a consistent 78 degrees.INDICATOR LIGHT: The red light shows when water is heating; green indicates that the heater is on standby.EASY TO USE: Just attach to an aquarium wall - the suction cup securely attaches heater to tank.SIZE: Use this 50-watt heater for aquariums up to 10 gallons - UL Listed.