JOLLY plastic heaters are designed for small freshwater, marine and turtles tanks. Their plastic casing makes them very durable and safe. These heaters can be placed beneath the gravel, making them a good choice for turtle or reptile tanks. JOLLY is always on when submersed. It stops working only when unplugged. The built-in thermal protection intervenes when the heater isn't under water, preventing overheating (LED light OFF even if Jolly is plugged in). Performance can vary according to the following parameters: - Quantity of water - Room temperature - Open or closed tank