Aqueon Pro Heaters are fully submersible Aquarium Heaters. The monitor lights let you know when the unit is heating with a red light or when the tank water has reached the desired temperature with a green light. This makes it simple to read without having to squint at the thermometer. With the quality put into this the electronic thermostat returns accurate readings that are within +/- 1 for the health and safety of your fish. They have a versatile arrangement options as they can be placed in your fish aquarium vertically or horizontally to accommodate different set-ups. They have a practically indestructible core of aluminum and no glass components making them long lasting! Also featured is a plastic covering, a large easy to adjust temp knob and suction cups for secure placement.