The only Apera pH electrodes that must be always stored in storage solutions and can be damaged if stored dry are the ones that use Polymer electrolyte, such as our probes for PH60S, LabSen 763 and LabSen 753. These Probes are made with a different type of material and over time will be damaged if stored dry.
For Apera's other regular glass bulb pH electrodes (like the ones for PH700, PH60 and PH20), users can store the probe in the storage solution to keep its sensitivity, which is a highly recommended good practice.
For our portable and benchtop pH meters, the pH electrodes come with a storage cap, which allows the elctrode to be soaked in KCL solution all the time when not in use. However, even stored dry, our pH electrodes per se will NOT "die". They just lose a bit sensitivity and accuracy temporarily. Users can always “revive” the sensor by soaking it in the 3M KCL storage solutions (the longer the better).
For pocket testers (e.g. PH20, PH60, SX610...), when not in use, users can just add a few drops of tap water in the probe cap to establish a humid atmosphere inside just so the sensitivity of the probe can be maintained. If the tester hasn't been used for a long time (>1 month), we recommend soaking the probe in the 3M KCL storage solution overnight to regain its sensitivity.
DO NOT soak or store any pH probes in purified water like distilled water, deionized water, or reverse osmosis water since it could cause damage to the pH electrode and the tester could give erratic readings. Rinse the probes in purified water is a good practice, just don't store them in purified water. If you accidentally store the probe in purified water, try store the probe in 3M KCL storage solution for 48 hours and see if the tester can perform in a normal state.
Other brands' storage solutions are NOT RECOMMENDED for use with Apera's pH electrodes, since they may use different formulas and could cause damage to the products.