pH meters employing a glass electrode are useful for precise pH
measurement in nutrient solutions. However, for reliable performance they
do require proper storage, handling and frequent calibration.
Obtaining pH readings with pH meters
Calibrate the meter.
Step 2. Sample preparation: Stir the
nutrient reservoir thoroughly before sampling, especially after pH Up or
pH Down is used. Ensure the sampling container is clean by rinsing a few
times with the nutrient solution.
Step 3. Obtain the pH reading: Rinse
electrode in distilled water before switching the meter on and immersing
in the sample. Note the following:
- When the pH electrode is first placed in a sample, it is common for the
reading to vary for some time (maybe several minutes) before resting on a
final/correct value**. Ensure to give enough time for the reading to
stabilize (Fig 10.4a). However, note the exceptions in the section “Preventing
** This can take several minutes especially if the sample’s
temperature is significantly different from ambient.
- Do not immerse the electrode in the sample to a depth that exceeds the
level of the filling solution inside of the electrode (Fig 10.4b). Since
it is not possible to view the depth of the filling solution (gel) in many
pocket sized meters, immerse the electrode to a depth of no more than
~20mm (3/4 inch). Exceeding this depth causes the sample solution to weep
back into the electrode itself. This will damage the electrode and cause
Step 4. If the pH is not between 5.0
and 6.5, adjust the pH of the nutrient
Step 5. When complete, rinse the
electrode with distilled water. For further information see “pH
Step 6. Store the electrode in a
proper storage solution when not in use. For further information see “Dry
storage of pH electrodes”.