Fully submersible glass heaters with thermostat control. These heaters offer a compact design for versatile placement and are extra durable due to the built-in glass element. The thermostat control makes it simple and easy to adjust the temperature settingand the sturdy guard helps to protect the glass heater from accidental breakage from large fish or turtles.. Aquatop’s HTG Series is suitable for both freshwater and saltwater use.