Fish Tank Heater Tips for Cold Weather


With colder weather moving in, it's a good time to make sure your aquarium heater is in good condition and working properly. With the exception of certain cold water species, most aquarium fish need warm water. Bettas, discus and certain other species do best in water that is between 76° and 85° F, most other tropical fish prefer a range of 75° and 80° F, and goldfish do best from 68° to 74° F. Water temperature should also remain constant to keep your fish's immunity up. This helps discourage diseases such as ich, which has a high mortality rate if not caught and treated early.

Below are some helpful and important tips for keeping your fish safe and happy over winter!

How Old is Your Aquarium Thermometer? Spot Check Often!

If your aquarium thermometer is damaged or is a few years old, it might be time to replace it. Stick-on LCD thermometers are the most accurate and easiest to read. Attach it on the outside glass, just above the gravel in a spot where you can read it easily and it won't be affected by direct sunlight, a furnace vent or other heat source. If possible, place it at the opposite end of the fish tank from the heater. Be sure to check the temperature regularly, daily if possible, to make sure the heater is doing its job.

Make sure your fish tank heater is in proper condition:

1. Check your heater size

A good rule of thumb for aquarium heaters is 5 watts per gallon for aquariums 55 gallons or smaller, and 3 watts per gallon for those over 60 gallons. Use a larger size or a second heater if your aquarium is in an especially cold room or is located on an exterior wall or near an outside door.

A list of aquarium gallon sizes along with heater wattage recommendations according to a 5, 10, and 15 degree increase of the water if the room is 68-72 degrees

2. Check the condition of your aquarium thermometer, are there cracks or other damage?

Unplug your aquarium heater and let it cool for at least 30 minutes before removing it from the aquarium. This includes flat heaters and those with plastic coated tubes. Replace the heater if any signs of damage or wear are detected. Remove mineral deposits or algae build-up to improve performance and reduce the risk of overheating. After returning your heater to the aquarium, wait at least 30 minutes before plugging it back in.

3. Check the indicator light

If you have an adjustable heater, check to make sure the indicator light is working. If the light is off, slowly rotate the control dial until the indicator it comes on and place your hand lightly on the lower portion of the heater tube to see if it is generating heat. Once satisfied the element is working, reset the dial to the desired temperature.

If you have an Aqueon branded heater, note that the Mini Heater and Aquatic Flat Heaters will not have an indicator light. The Aqueon Preset Heater will only show an indicator light while it is heating up the water.

4. Consider the right placement for your heater inside the aquarium

Position your heater near a filter inlet/outlet or a circulation pump to ensure even heat distribution. Submersible aquarium heaters can be installed horizontally near the bottom of the tank for best results. They can also be positioned vertically if that is your preference. Keep decorations away from the heater so water can circulate freely around it.

5. Know the right way to make temperature adjustments

Compare the heater setting to your aquarium thermometer reading. Controllable heaters may need to be further adjusted to achieve the desired water temperature, depending on the location of the aquarium, ambient room temperature and water circulation. Avoid placing your aquarium near a drafty location such as a door, an uninsulated wall, or cold basement. If you do, you may need a second heater and you may also need to adjust them more often. When your making adjustments to your heater, allow several hours before checking the results. Do not change your aquarium's water temperature suddenly or dramatically, as this can stress your fish!

Here are some additional important safety tips:

  • Always unplug your heater and let it cool for at least 30 minutes before removing it from the water
  • After installing your heater in the aquarium, allow at least 30 minutes before plugging it in
  • Always use a drip loop and make sure the cord and plug are dry when plugging your heater in
  • Visit our list of DO'S and DON'TS to make sure that you are following all the right steps!

Are you looking for more helpful facts and information to keep your fish happy and healthy?

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