Most tropical fish are warm water fish and need a constant warm temperature in the aquarium for the fish to be healthy. Aquarium heaters provide a way to maintain desired water temperatures to meet the needs of the fish. The heaters usually have a built in thermostat so that changes in water temperature can be detected and the heater can turn on or off as needed.
There are many different types and brands of heaters available to choose from. When choosing a heater, you should make sure you get one that is going to be big enough to adequately heat the water of the aquarium. Get one with the right power rating to fit the size of the tank it will be heating. A good option is to use 2 slightly smaller heaters in the case that if one fails the other will be able to keep the water temperature acceptable till a replacement can be bought.
