# Temperature fluctuations with new heater



## waterlilly (Aug 22, 2010)

I have a Eheim Jaeger Trutemp heater for my small tank. I noticed that there are temperature fluctuations. The temperature goes between 25.4 to 26.3. I don't think I've ever encountered this before. Is it possible that I set it too low? Meaning it doesn't kick in until the temperatures reaches 25.4? If I were to raise it, would that not mean that it would get warmer than 26.3? I'm really confused.


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## TomC (Apr 21, 2010)

When does it hit the higher temperature? Could the temperature be set at 25.4, but the light or something be raising it above that during the day?


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## The Guy (Nov 26, 2010)

Try to recalibrate it if it's an older heater, google or u-tube it for how to do it.


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## waterlilly (Aug 22, 2010)

TomC said:


> When does it hit the higher temperature? Could the temperature be set at 25.4, but the light or something be raising it above that during the day?


It changes throughout the day. When I turn on the light in the evening, I usually open the lid a tad.


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## waterlilly (Aug 22, 2010)

The Guy said:


> Try to recalibrate it if it's an older heater, google or u-tube it for how to do it.


I bought it a couple of months ago. But I will try to re-calibrate it this weekend.


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## kivyee (Oct 15, 2016)

Is your issue with the temperature variation? That's the inherent hysteresis in the internal temperature switch. This is a characteristic of controlling an on-off device to a set-point. 
There needs to be band - a "turn on" temp and a "turn off" temp. It likely won't get too much better unless if you go with an external controller, but then you will be cycling your heater on and off a lot to try and hit a narrow temperature band. I would say unless if you have some super sensitive fish, a 1 deg C variation is nothing to worry about.


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## waterlilly (Aug 22, 2010)

kivyee said:


> Is your issue with the temperature variation? That's the inherent hysteresis in the internal temperature switch. This is a characteristic of controlling an on-off device to a set-point.
> There needs to be band - a "turn on" temp and a "turn off" temp. It likely won't get too much better unless if you go with an external controller, but then you will be cycling your heater on and off a lot to try and hit a narrow temperature band. I would say unless if you have some super sensitive fish, a 1 deg C variation is nothing to worry about.


I was paying a bit more attention yesterday evening. The temp goes down to 25.4, the heater kicks in until it the temp is at 26.2. So a variation of almost 1 degree numerous times a day is nothing to be worried about? I just don't understand why my simple Aqueon heater kept the temp in the 5 gallon at a steady 25.8. I'll try to re-calibrate it this weekend and see if it changes anything. I might just change heaters...


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## TomC (Apr 21, 2010)

Personally, I wouldn't worry about 1 degree.


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## dino (Aug 29, 2011)

If you are anal about temp swings I’d recommend what I always do and that’s a temperature controller with a titanium heater. I normally spend 100.00 for the unit and heater and it lasts years without issue. Also the temp will swing .02 of a degree between off and on.


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