Profile: Beginner Aquarium is an online store for aquarium supplies. Non-submersible heaters are also called hang-on heaters, which consist of a metallic element controlled by a thermostat and enclosed in a glass or metal tube to prevent contact with water. Chiller units are used to automatically regulate the water temperature of saltwater and reef tank systems. Submersible pumps are run completely underwater, usually in the sump of a wet/dry filtration system. They draw water from the filter, and push it back into the aquarium, or through other devices, such as chillers or UV sterilization units. They are easy to install and tend to be a little quieter because they run underwater. Tank heaters keep a stable water temperature inside the aquarium despite the cold temperature outside. Water heaters come in many kinds. Some heaters are automatic and include a built-in thermostat to select the optimal temperature, while some require the use of thermometers. Most aquarium heaters are immersion style heaters while some are integrated within filters. There are also undergravel heating units that can be buried beneath the aquarium substrate, and heating mats that are placed under the aquarium.