You may have already mentioned this in previous posts, but have you validated your ORP results using a different probe?In my pool orp rises as the pool gets shaded and drops as the sun hits it. Something to do with the chlorine cya interaction to sunlight. The less cya I run the greater the orp swing. It’s a rhythm that repeats every day. I run my pump 24/7. It happens even in the winter here as well. Also if I run my waterfall orp rises a lot. So many things affect it. Today my orp ranged from a high of 665 just before sunrise to 570 just prior to when the sun ducks behind some big trees and shades the pool. My cya is 15 and fc was 5 ppm.