My Heater Won't Heat My Fish Aquarium

Successful hobbyists know that the key to keeping fish is to recreate the natural environment as closely as possible, and maintaining the tank at the proper temperature is a big part of that. In order to stay happy and healthy, the fish in your aquarium must thrive in a specified temperature range. For instance, the African cichlids native to Lake Malawi generally require a temperature between 78 and 82 degrees Fahrenheit, similar to the conditions they would find in their natural home. Mollies, swordtails and other livebearing fish do well in temperatures between 80 and 84 degrees.

Things You'll Need

  • Aquarium
  • Heater
  • Thermometer
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Instructions

    • 1

      Move the heater away from the power filter. The constant stream of water returning from the power filter can reduce the effectiveness of the heater.

    • 2

      Place thermometers in several different sections of the tank, especially if you have a large aquarium. Occasionally, the temperature will be fine on one side of the tank but not on the other side.

    • 3

      Add a second heater on the other side of the tank if the temperature is warm enough on one side but not the other. Large tanks often require several heaters to keep the entire tank at the proper temperature.

    • 4

      Unplug the heater and remove it from the tank. Check the top of the heater for a temperature dial. Many modern heaters include a dial hobbyists can use to set the desired temperature. If your heater does not, consider replacing it with one that does.

    • 5

      Buy a heater rated for at least the size tank you have. Using a heater that is too small will result in uneven heating. It is often better to buy a heater rated for a tank larger than the one you have. For example, buy a heater rated for a 30 gallon tank to use in your 20 gallon aquarium.