I had brought mine up to 80 in a couple different increments due to installing a SWG this year. I started with fresh refill testing regents I purchased from TFtestkits, stored in a closet in my home. A friend had stopped over & was present when testing the 80 figure, we both did the test independently with multiple pour-backs to verify the 80 level. It came out everytime with us both to be a solid 80. Perfectly clear, sparkling water & two weeks later I tested again. Again multiple tests, under 50 (I guestimated 45) every time. I had just enough HTH stabilizer (purchased from Wally World this spring) to get me back to 60 per the pool calculator. I waited a week, sure enough it was back to 60 after multiple tests. No fertilizer, roundup, or algae bloom during that time. The only thing that might have been a factor, is in a nightly testing with the chlorine/ph test block, one time during the period I came up with a 1 fc. I checked the cell, everything was fine, water was still very clear with no signs of algea, dumped in one 182 oz jug of 6% to put me back up to around 8, the SWG since has had no trouble maintaining a 5 ish FC level & previously had no trouble before. No extreme chlorine demand after the incident, so I can't see the ammonia conversion happening. Everything's been fine since, but for kicks I'm going to do another test tonight to see if the 60 is holding. Your thread just caught my eye, because this is what I experienced. No catastrophe for me, but very puzzling.