pH electrodes do not last forever!
The life of your pH electrode is not infinite. A number of factors affect the life span of your pH electrode. The higher the temperature that the electrode is used at, the more extreme the pH, how often the bulb dries out and needs to be rehydrated, how roughly it is used; all these factors and more shorten the life span of your electrode.
An electrode that is well maintained and cared for can last up to 2 years, one that is not well maintained will not last as long, and one that is well maintained will not last significantly longer.
Storage of the pH electrode when not in use.
The pH electrode bulb needs to be moist at all times.
When you are done with the electrode pour electrode storage solution into the cap that came with the electrode and put the cap over the bulb of the electrode. Keep the cap on until next use. If the electrode is being stored for a long time you may want to check the cap to be sure the storage solution is still in the cap and keeping the bulb moist.
DO NOT STORE THE pH ELECTRODE IN DISTILLED WATER. Storing the pH electrode in distilled water will shorten the life of your pH electrode.
Rinsing the pH electrode between measurements.
You should rinse your pH electrode between measurements. This can be done with distilled water or rinsing with a sample of the next solution to be measured. Using both distilled water and then a sample of the next solution is also a good way to rinse the pH electrode between measurements.
pH electrode fill hole.
Some pH electrodes have a fill hole for refreshing the electrolyte in the pH electrode; other pH electrodes do not have a fill hole. If your pH electrode has a fill hole the fill hole cap should be removed during calibration and use. This allows for the correct amount of reference electrolyte to flow into the sample. Replace the fill hole cap when done with the electrode at the end of the day.