The 26419-05 50 W Submersible Aquarium Heater comes with a pre-set electronic thermostat that automatically maintains an ideal water temperature of 78°F (±2°), and reduces the risk of overheating Requiring no manual adjustment, the water heater even features an indicator light that turns red when the water is heating, and green when the water is at the ideal temperature The heater is made of heat- and shock -resistant borosilicate glass, making it durable and guaranteed to last a long time Ideal for aquariums with capacities ranging from 10 to 30 gallons (37.8 to 113.5 liters), the heater is specifically designed to be completely concealable so that your aquarium's total look is preserved