The pH glass bulb of probes should always be kept in an aqueous ionicsolution, preferably with an excess of hydrogen ions, to maintain hydration andprobe response. For long term storage (overnight or longer), the probe should bekept in storage solution using a rubber boot. This " wet storage" alsoprevents the reference frit from becoming clogged with crystals from the fillingsolution. The reference refill hole may also be closed to prevent evaporation ofthe filling solution. Never store your electrode in distilled water. Read themanufacturers recommendations for the most accurate storage advice.