The temperature of your aquarium is an important factor in the comfort and well being of your fish. Unlike humans and warm-blooded animals, fish do not produce their own body heat. They must rely on the temperature of the water to maintain their body temperature. Maintaining the temperature in a constant level can be accomplished by using proper heaters. There are four basic types of aquarium heaters : 1) Immersible heaters 2) Submersible heaters 3) Under Gravel Heaters 4) Filter heaters. The choice of the heater should be made according to your requirement. There is a way to calculate the size of the heater you would need for your aquarium from the room temperature. The heat mentioned below is the difference between the room temperature and the optimal temperature for the fish. Tank Capacity Heat 5 Degrees C 9 Degrees F Heat 10 Degrees C 18 Degrees F Heat 15 Degrees C 27 Degrees F 5 gal/25L 25W 50W 75W 10 ...