Not sure if this should go here or under hot tubs/spa. I maintain a 800gal hot tub for a members only gym that typically runs 16-18 hours a day. The sanitizer and Ph levels are maintained with a Polaris Watermatic C660. The ORP sensor is around 6 months old and the Ph sensor is pushing a year. Over the last two weeks the readings on the C660 have gotten continually lower and lower (especially on the ORP side). I have lowered the feed setting to try an keep the ORP level around the 5.0 range and have adjusted the calibration on the Ph sensor as low as it will go, yet I am still getting slightly high ORP and low Ph. I have tried cleaning the sensors with white vinegar as the manufacturer recommended and while it will help for a few hours, they always revert back to reading low. Is it time to replace the sensors again or is there something else I can try to get them to read correctly?