This troubleshooting tip is meant for Eutech's DO Self-stirring probe which is used in the premium CyberScan DO5000 and PCD5500 series bench meters.

Clean the probe as per the instructions. Sand the gold cathode and soak the silver anode in 14% ammonium hydroxide for 3 min. Replace the membrane cap and add fresh electrolyte.

If the calibration value is still not satisfactory, clean the probe again. This time use 400 grit fine sandpaper. 

Wrap the sandpaper around the silver anode and turn in a circular motion to remove a white precipitate that can result from ammonium hydroxide soak. Wash again with deionised-water.

Now recalibrate and test the electrode again.

If aggressive cleaning does not work, the sensor assembly can be replaced (Contact Eutech Instruments for further information).