Why does my aquarium heater get too hot?

Jul 3

I have it set on the lowest setting and it keeps on heating up to 85 degrees. Is it defective or do I need to do something different? It’s a 100 watt heater in a 20 gallon tall freshwater tank with an airstone and whisper power filter that really churns up the water?

Heater size should not matter since it is set at a set temperature and when the water reaches that temperature it is designed to turn off. I would get a new heater here. It apparently is not functioning properly.

I would worry that it will go totally bad and kill off the fish

Can i make my aquarium heater more energy efficient by only using it at night, then unplugging during the day?

Filed under: Aquarium Heaters

5 Responses to “Why does my aquarium heater get too hot?”

pyle221, on July 3rd, 2009 at 10:58 am Said:

Can you re-calibrate it? If not buy a new one. It’s gonna cook your fish.
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Mike, on July 3rd, 2009 at 11:16 am Said:

It may be how you have positioned it in your tank. It should be diagonal, otherwise the thermometer may take readings from the heater’s output etc.
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Stephanie, on July 3rd, 2009 at 11:29 am Said:

it’s probably either broken or you have too big of a heater, you may need to go the next size down. does it get a lot of natural sun light? that can heat up the water too.
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Drew, on July 3rd, 2009 at 11:59 am Said:

Unfortunately, aquarium heaters have a high rate of failure mainly due to the malfunctioning of the internal thermostat. Depending on how old your heater it may still be under warrenty otherwise you’re going to have to get yourself a new heater. Good luck.
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danielle Z, on July 3rd, 2009 at 12:39 pm Said:

Heater size should not matter since it is set at a set temperature and when the water reaches that temperature it is designed to turn off. I would get a new heater here. It apparently is not functioning properly.

I would worry that it will go totally bad and kill off the fish
References :

Aquariums 2.0