Fish Tank Heaters

The Heat Is On

Tropical and Marine Fish require temperatures of about 78 degree or higher (82 degree for discus). To achieve these higher temperatures and sustain them in an aquarium, heaters are used. Aquarium heaters have a variety of features and elements that help them function. It is important to know that the temperature within an aquarium should only ever fluctuate 1-2 degrees in a 24 hr period, so make sure the heater you choose is reliable.

Types Of Heaters


Submersible heaters are completely under the water. They are usually placed at an angle so that a lower water level won't cause them to break. (If a heater is functioning under water and then taken out of the water, it will usually break because of the sudden temperature change.) These heaters are also usually placed under the filter output so that the water entering the tank is heated just as it enters the aquarium. This helps to evenly heat the tank.


Hanging heaters hang over the side of the aquarium like a filter, although the heating tube is inside the aquarium. The temperature dial usually sits right on the hanging part. As with the heaters above, you will have to make sure the water level never drops down to the glass part of the heater, it might break!


External/Inline heaters are connected "in-line" with water pumps, etc. The water usually comes through the filtration and is on its way back to the main tank when it passes through the "in-line" heater, where it is heated to the appropriate temperature before it gets back to the aquarium. This type of heater is great if you have aggressive fish that may damage an internal heater. In-line heaters are also more accurate, insuring your temperature does not fluctuate.

Installing & Using Your Heaters

Most heaters include suction cups to keep them against the side of the aquarium.

The temperature dials vary greatly on all models. Some simply have a dial that can be turned + or -. In this case, a customer must rely on a thermometer to tell the temperature and for making any adjustments. Other heaters have pre-selected temperatures that you can just switch the dial to, and supposedly the heater will reach that temperature and maintain it. Of course, nothing is perfect, so a thermometer should also be used to make sure the heater is staying at its set temperature! Make sure you allow the heater to sit in the water for a few hours before turning it on, so that the glass can get used to the water temperature, and won't break.

Choosing A Heater For Your Aquarium

A basic rule of thumb is 3-5 watts per gallon. To heat a tank thoroughly, and maintain that temperature, the heater must have enough power, i.e. wattage, capable of affecting the number of gallons in the tank. If a 100 gallon tank only has a 100 watt heater, that's 1 watt per gallon, which is not enough power to keep the temperature where it needs to be.

An example would be:
  • -A 65 gallon aquarium will need a heater capable of about 200-300 watts.
  • --65 x 3 watts/gallon=195 watts total
  • --65 x 4 watts/gallon=260 watts total
  • --65 x 5 watts/gallon=325 watts total

  • * We recommend you use 2 heaters rather than one super-strong one.
    Make sure you aren't purchasing a heater that is much too strong for your aquarium. A 100 watt heater will certainly be too much for a 10 gallon aquarium!