I'm using an Eheim thermocontrol 50W thermostat in my 60l freshwater aquarium.

The official manual and dozens of forum posts state that the temperature is set by turning the outer blue wheel to the desired temperature and then correcting it with the red calibration wheel in order to compensate sensor deviation. All information I could find is numerous repetitions and reformulations of this information.

It's not possible to set the initial temperature with the blue wheel since it's doesn't have any anchor point, thus any number at any position on the wheel could mean the currently set temperature.

Approaches like trial and error (for the initial temperature) are not an option since that'd mean endless combinations together with the red calibration wheel.

1 Answer 1


You simply turn the red ring fully counter-clockwise and then turn the numbered ring, so the red arrow points at the temperature you want in your tank.

By doing it this way you will avoid overly high temperature in your tank during calibration. So you will probably have to turn the heat up a bit after you have adjusted the red arrow.

Use a thermometer in your tank to see what temperature you get, it takes a day or two to see where the temperature ends up at.

You can now turn the red ring, so it points to the real temperature you have in your tank.

You have now calibrated the heater scale.

It is best to keep an eye on the temperature during this calibration and turn the numbered ring down if it gets too hot in your tank (take a look at the temperature every four to five hours during this process).

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This is how it looks with the red ring turned fully counter-clockwise and the temperature set to 23 °C, on my heater I do not need to move the red ring at all as this is the real temperature (I plan to use this tank for shrimps so this is why I have the temperature this low).

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