Does chlorine lock exist? I've read several threads which seem to say yes, and no. My 17,500 gal IGP was reading 20 FC and TC, 7.2 PH, and CYA through the roof at 150. With no chlorine granules or tabs in over 2 weeks, these numbers sadly stay consistent. I've been draining as much as I can (no drain, pump to waste via skimmer) and refill, numbers are getting slightly lower on CYA after my 3rd attempt but not fast enough. I'm on a well out in the country so I've striked a good balance of drain/refill that my well seems to handle just fine. I've raised my CA to 400 and attempting to try ez-pool to bind to the calcium while I continue to drain/refill twice a week. I did neutralize the chlorine levels (via an oxidizer) to get them lower which works. Any other advice/method I should explore using here in this situation?