Took the winter cover off on Sunday to find a full to the gunnells pool and a for the most part viable solar cover! The only differences in the 8 years prior, asside from it being full, was some clearish slime, and extremely low ph--below the lowest measurable amount. I'm on my 3rd box of Borax and it's only up to 6.5! Initailly added a 121oz jug of bleach, 2 hours later--no measurement, added another jug 8 hours later--no measurement, added 3/4 of a third and have been holding steady. Alk is 80, didn't test for calcium as it's a vinyl pool. Assuming the low PH hasn't caused any damage to the vinyl liner, I may do this every year.