When choosing a heater for your fish tank, it's important to get a good reliable unit since fluctuations in temperature can be fatal to fish. You'll need to about 5 Watts of heater or for each gallon of aquarium water so a 20 gallon aquarium would need a 100 Watt heater. for large aquariums it's better to divide up the load and have a heater on each side of the tank so that the water heats up evenly. If you keep your room really cold, you might want a higher wattage heater since it will have to do more work to keep the water temperature between the 75 and 79 degrees Fahrenheit that most tropical fish prefer.

There are two kinds of aquarium heaters to consider, the submersible heaters and the hang on heaters. to hang on heaters are named such because they hang on the side of the tank. The entire heating unit does not go underwater and the controls stick up with the glass part going under the water This is not as efficient or as precise as the fully submersible heater which can be fully submerged under the water. The submersible heater sticks to the side of the tank with section and gives you more precise heating and also the option of hiding it below plants or decorations.

When buying an aquarium heater, you want to also make sure that you have a thermometer either built into the heater a separate so that you'll know the temperature of your tank. This temperature should always be monitored as if the water is too hot or too cold this can be very detrimental to your tropical fish. If you notice large fluctuations, it could be time to get a new heater. Another thing you might want to consider is having two heaters and keeping one in reserve in case the one you are using breaks. This way your fish will not have to suffer until you can get out to the pet store to get them a new heater.

Since tropical fish are cold-blooded, they cannot maintain a body temperature and must depend on you to heat up their water for them. Making sure you have a good functioning aquarium heater will help keep your fishes environment as close to that which they are used to in nature and reward you with happy healthy fish that look great in your aquarium!