pH meters work by sampling the concentration of hydrogen ions in a solution with a probe that has a delicate tip made of very thin glass. To get accurate measurements, this probe must be treated gently and be carefully and regularly cleaned and calibrated.

The best advice is to follow the manufacturer’s instructions for your meter, but here are some general recommendations.

Cleaning: The best way to clean the tip of a pH meter is not to let it get dirty in the first place. Probes that are left immersed in solution should be shielded from light to prevent the growth of algae and placed in the cleanest part of the solution that is still representative of the overall pH.

Calibrating: Here is a typical calibration procedure:

1. Place the probe in a sample of pH 7.00 calibration buffer. Adjust the meter for a pH of 7.00.
2. Rinse the probe with distilled water and then gently blot the tip with a tissue to prevent solution carryover.
3. Immerse the probe in pH 4.00 buffer and adjust the pH meter so it gives a reading of 4.00.
4. Rinse the probe and blot, repeating steps 1 to 3 until readings are stable and no further adjustments are necessary. Usually a couple of repetitions are sufficient.

Storing: The probe tip must be kept wet at all times and should be stored in buffer solution when not in use.