Piensa en verde offers you spare electrode Hanna PH Mod: HI 7630.
This electrode has a sensor based an electrochemical cell. This cell begins to suffer wear from the time of manufacture to the end of its life. The life of an electrode is limited, with the typical 1 year to 2 years.
It is essential to careful management and good housekeeping for a good result in measurements. Never touch the electrode fingers, paper, or anything other than water.