Aqueon Preset Aquarium Heaters require no adjusting The preset temperature has been calibrated to 78?, appropriate for most tropical fish. It is fully submersible, constructed of shatter-resistant quartz glass and features an automatic safety shut-off to avoid overheating. The heaters include suction cups and can be placed vertically or horizontally within the aquarium. An LED indicator light displays red when actively heating. Available in different sizes to accommodate all aquarium sizes. Aqueon products offers a wide range of items so that you can build and maintain a healthy aquatic environment. All the essentials from fish tanks, filters, lighting, food, care, and other supplies that your pet fish needs. We make it easy for you to get your first aquarium and to grow in the hobby as you become more of a fish expert with every step you take and every new thing you learn. For those seasoned hobbyists, we are committed to aquarium product innovation so that we continue to offer products that get you excited. With the Aqueon brand, it's all about the fish. Preset to 78?, accurate to +/- 1?. No adjustment required. Shatter resistant. Auto shut-off. LED light turns on when aquarium water is being heated. Ideal for aquariums up to 55 gallons.