JOLLY heaters are designed for small freshwater and saltwater aquariums. Their plastic housing makes them very durable and safe. JOLLY heaters can be placed under the gravel, making them a good choice for turtle or reptile tanks. The JOLLY heater is always in operation when it is submerged. It is only deactivated when it is disconnected. The built-in thermal resistance intervenes when the heater is operating out of the water and overheating is prevented (the light is only off when JOLLY is not in operation). The performance depends on various conditions: - Water volume - Room temperature - Open or closed aquarium.