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Sensor probes require periodic cleaning, reconditioning and calibration for reliable service.
See calibration section for details on performing calibration service after cleaning.
Maintenance
Probe Cleaning
Coating of the pH or ORP bulbs can lead to erroneous readings including short-
ened span (slope). Coatings and blockages in the EC sensor can cause incorrect
readings. The type of coating will determine the cleaning technique.
Soft coatings can be removed by vigorous stirring or by the use of a squirt
bottle.
Organic chemical or hard coatings should be chemically removed. 5-10% hy-
drochloricacid (HCl) soak for a few minutes and often removes many coatings.
If cleaning does not restore pH sensor performance, reconditioning may be
tried.
Do not use a brush or
abrasive on pH or EC
probes.
pH Probe Reconditioning
When reconditioning is required due to electrode aging the following chemical treatments can be tried.
They are presented in the order of the severity of attack on the pH glass and may not improve (and in some
cases actually further deteriorate) electrode performance.
DANGER: Use proper precautions when handling these hazardous chemicals. Ammonium bifluoride and
HF (hydrofluoric acid) are extremely hazardous and should only be used by qualified personnel.
Reconditioning Method 1
Immerse the electrode tip in 0.1 N HCl for 15 seconds, rinse in tap water and then immerse tip in 0.1 M NaOH
for 15 seconds and rinse in tap water. Repeat this sequence three times and then recheck the electrode’s
performance. If performance has not been restored, try method two.
Reconditioning Method 2
Immerse the tip in a 20% solution of NH4F-HF (ammonium bifluoride) for two to three minutes, rinse in tap
water and recheck performance. If performance has not been restored, try method three.
Reconditioning Method 3
Immerse electrode tip in 5% HF for 10-15 seconds, rinse well in tap water, quickly rinse in 5N HCl, rinse well
in tap water and recheck performance. If performance has not been restored, it is time to get a new probe.
