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I have a Tetra Whisper Heater 20 (100 watts) in a twenty gallon tank. It seems to lose track of what temperature I set it at. If I set the heater at night, and leave it set over night and throughout the day, it still occasionally comes on during the day, even though the water is warmer than it was when I originally set the heater. I just think it's not good for my fish to have to deal with fluctuating temperatures, and I'm kinda sick of having to reset the heater every night. Does anyone know if I'm missing something, or if I just need to invest in a better heater?

Most heaters have a natural fluctuation, but it shouldn't be more than a couple of degrees. Also, most heaters' dial for temperatures is off as well, so you'll have to set it manually by using a thermometer floating in the tank. How many degrees is the heater fluctuating by? If you turn the heater down a few notches and let it sit overnight, will it stay constant? What do you have the temperature set at now?

At night, the ambient temperature in the atmosphere around the tank will drop, and so does the water. The heater will come on a little bit more often at night, but it shouldn't be on constantly. Water has a high specific heat, so it takes longer to heat and cool. Also, most fish tanks are set to a higher temperature than ambient, so they are constantly losing energy attempting to go down to ambient, so your heater will come on every so often to keep it constant.

Or, like you said, you could have a defective or poor quality heater that just doesn't do it's job properly. A backup might is never a bad idea in case your current heater decides to malfunction.

Hi there little fish,

I hope I am not talking to myself, as I am LITTLE_FISH .

I don’t have a Tetra Whisper Heater (I didn’t know the others make noise) but can you explain your concerns with the addition of temp degrees? I mean, what are we talking about here – 1 degree or 10?

If you do not adjust the heater temp, then what is the temp in the tank in the evening just before the lights go out, midday, and in the morning just before the lights come on?

If you talk about a 1degree difference, then there is no problem.

Ingo

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Proud Member of the New Jersey Aquatic Gardeners Club

The problem is not that the temperature just fluctuates a few degrees. It seems like the temp increases over time. The heater will seem to be working just fine, but after a day or two the temp has gone up five degrees or so, and the heater is still coming on. It's like the heater forgets that it's set at a certain temperature and just keeps coming on even though it's way warmer than it should be.

To be on the safe side toss it out and get another one it sounds like a faulty contact point in the setting. Just think what will happen if it forgets to turn off completly.
I think it is called cooked fish.

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Keith

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I agree with our blue buddy down under, toss it. The heater is often referred to as the most important piece of equipment in a fish tank, so you can't chance it.

thanks. that was pretty much my thinking too. i plan to go to the pet store right now and get a new one. i've already lost several fish, and i am beginning to think it is mostly due to temp fluctuation. thanks again for the help.