An aquarium heater is one of the most vital pieces of equipment required in caring for your fish. Because fish are cold blooded, they depend solely on their environment for body temperature regulation. Maintaining the proper temperature in your aquarium ensures that your fish will remain healthy and stress free, thereby reducing the chances of bacterial infection and possibly death. Certain species of fish live in specific and localized regions of the globe to suite their own individual temperature tolerances, as well as food sources, and habitat. Of course, meeting the temperature preferences for your fish depends on the particular type of fish in your aquarium; however, barring the most exotic species, most fish found in aquariums are tropical and thrive in temperatures ranging from 77F to 83F degrees and for saltwater fish tanks the range is 76F to 82F degrees, I personally keep it at 79F to 80F degrees. To accurately measure the temperature in your aquarium, a temperature strip which is adhered to the exterior of the tank, or a floating thermometer should be used.
The three most common methods of heating aquariums are under-tank heating, under-gravel heating and glass immersion heaters. Under-tank heating, in which a heating mat is placed beneath the floor of the aquarium, is the least efficient method. This technique is generally not recommended, as glass is a poor conductor of heat, therefore resulting in heat loss and far less reliable temperature control than obtainable through under-gravel or glass immersion heaters.
Under-gravel heating consists of a flexible heating element that is buried beneath the aquarium gravel or sand. Having the element buried beneath the aquarium gravel is particularly beneficial in tanks with a high concentration of plant life because it does not interfere with the growth of the plants.
Glass immersion heaters are perhaps the most popular devices for heating aquariums. These types of heaters consist of a heating element and an adjustable thermostat encased in a glass tube which is fully submersible.
The general guideline for choosing an appropriate aquarium heater is 3 Watts of power per 1 gallon of water. If your aquarium holds 100 gallons of water, that would be a 300 Watt heater. If the wattage you need falls in between two heater sizes, it is generally best to choose the more powerful heater, or to use two smaller heaters to ensure proper heating of your aquarium. The advantage of using two smaller heaters is that in the event one heater malfunctions, the second heater can compensate by maintaining an acceptable temperature in the aquarium until the problem can be remedied.