Oops, sorry. I thought I was replying to the OP.I have two probes and they are calibrated about every 6 months. Over the last several years each has been replaced more than once. Again though this is not an issue for me i resolved this many years ago with an outside air skimmer line. At times i have disconnected the (usually accidently) and the ph starts dropping. In fact when i see low ph the first thing i check is if the airline is still on. The reality is for many people this is a big issue easily fixed with outside air. For many others there is no issue(or there is an issue that outside air wont fix). Just depends on each situation.
I run at a higher than average dkh between 10.5-11.0