I've used brand x for several years. I just had to toss the original probe due to the wire "coax" going to the probe wore out. The shield where it enters the probe top broke. So readings became erratic. It was sealed so I couldn't replace the cable. I've left the probe uncovered numerous times for 24 hours. In the beginning I rinsed it with ro water then slung the water off and stuck it in the solution. Either I'm lucky or the probes are pretty tough. I'm on my second now after 3 years plus. The new probe didn't need calibrated to the meter. The 7.0 and 4.01 solutions read dead on.