Sensing Bulb
The glass bulb loses sensitivity with use and will eventually fail. This is true of all pH probes.

Reference Junction
The reference junction is a small hole that allows the meter to compare the sample to a reference. The reading is generated based on the electrical difference between the sample and reference. If the junction hole gets clogged, the pH probe will no longer function.

You can extend the life of your pH electrode in the following ways.

Cleaning and Storage
All pH sensors have a limited life and response time gets longer with age. Properly maintaining your pH pen tester will give you fast, accurate results for longer. So, be sure to order the Milwaukee pH Maitenance Kit code PH-Main at checkout time!  This will be needed to help clean and condition the pH electrode before use!

Storage
The pH probe needs to be kept hydrated. Long periods of dry storage will damage the sensitivity of the probe. Allowing the probe to dry out may also result in the junction hole getting clogged.

Storing in pH probe storage solution MA9015 or pH calibration buffers will help address both these issues. Do not store in tap water and DI water. This will damage the sensitivity of the probe.

The best way to store the probe is with the probe's cap filled with storage solution or calibration buffer and the cap tightened to prevent leakage. It is also recommended that to store the electrode upright to further reduce the potential for leakage.

Cleaning
Residue from the sample can impact the sensitivity of the sensing bulb and clog the junction. This is especially true if the sample has a lot of organic material. We recommend regularly soaking your electrode in cleaning solution MA9016.

Calibration
The pH sensing bulbs become less sensitive over time so make sure that you are calibrating reguarly to keep your PRO pH meter accurate. Also, calibrate after cleaning or a long period of storage.