Aquacontrol CL2 Deluxe WiFi 2,4 Mode D'emploi page 40

There are a number of potential causes of calibration errors:
You have used the same buffer solution twice during calibration. Correct
calibration can only be carried out with two different technical buffer solutions.
pH 7 first and then pH 4.
The measuring cable was connected incorrectly. The pH probe must be connected
to the left socket.
The buffer solutions are exhausted. Try again using fresh buffer solutions.
The measuring cable is defective or not connected. Please check the connection
between the electrode and the control unit.
The pH probe is worn. The lifetime of a measuring electrode can be influenced
by quality of the water and care.
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