<P> An aquarium heater is a device used in the fishkeeping hobby to warm the temperature of water in aquariums . Most tropical freshwater and marine aquariums are maintained at temperatures that range from 22 - 30 ° C (71 - 86 ° F). The types include glass immersion heaters and undergravel heating . There are also heating mats that may be placed under the aquarium . </P> <P> Most commonly, aquarium heaters are immersion style heaters, these heaters consist of a glass tube containing a heating element wound around a ceramic or glass insert . Some glass immersion heaters also contain sand, and most, but not all, are fully submersible . The glass tube also contains an adjustable thermostat which turns the heating element on to maintain the required temperature . This thermostat is often a bimetallic strip; because the strip contains two metals, the metals will expand at different rates when the temperature rises, causing the strip to bend . This strip carries the current, but breaks the current at the correct temperature . The setting of this bimetallic strip can be adjusted . More advanced thermostats may use microchip technology . A small light in the heater is often included to indicate operation . </P>

What is the use of heater in aquarium