Having drained down to just below the skimmer frame and refilled - I still have the CYA at 7/16" below 100. So I did 50/50 tap/pool water and get 94. My chlorine today, the basic test, is just orange and not dark and did not turn that dark instantly as it had been. Ph is at 76. Still must dump and replace more water I reckon. In ALL my years of caring for an above ground pool (the first one was 18k, 18 x 33 - not as deep) I have NEVER run into this before :-(