Scott, I misplaced the first cap shortly after purchase and began using the second. We found the misplaced one soon after and following my son's suggestion soaked it in hard contact lens solution, rinsed thoroughly and stored it in a vial filled with the solution it came with. About 20 months later now, I just checked and they both look good as new to me. Unlike the pH and ORP probes, I don't think the O2 probe is as sensitive to scratches but it should be kept from drying out by keeping it in solution when not sampling. And I think a gentle soft bristle brushing when calibration or reaction seems slow is effective in preventing scale build up.
Scott Roberts said:
Glen - how often do you need to change the membrane on your pinpoint meter?