I have been dealing with a fair amount of difficult pools this season, many of which require significant amounts of chlorine to reach shock levels due to high Cyanuric Acid levels. Just about every time I straighten out one of these pools, my boss questions the high FC levels out of fear that we might bleach a liner. So I have been wondering if anyone has seen any data showing just how much chlorine it would take to bleach a liner.
I put together a little mini experiment to get a rough sense of how risky it might be. I took a scrap piece of liner, and I cut it into small strips. Then I took four 1 liter bottles and filled two of them with water containing approximately 100ppm FC, and added a strip of liner to each. The other two were filled with water containing about 50ppm FC. Then I took one of each concentration and added a small amount of CYA to them. So I have 50 and 100 ppm FC with and without CYA. I put the bottles in a bucket on my back porch and covered it so the sun wouldn't affect the FC.
After a week, I opened the bottle with 100ppm FC and no CYA, the worst case scenario, and verified that the FC was still at 100ppm, and it was. I didn't see any noticeable fading of the liner. I didn't take the liner out of the bottle because it would be a bit of a pain to do, so it is possible that there might be a small amount of fading, but I intend to compare it side by side in a few days, which would be two weeks. I think that if I don't see any fading after two weeks at 100ppm FC and no CYA, the risk of bleaching a pool during a Shock or SLAM is non existent up to 100ppm FC, which is way higher than the necessary FC levels in the vast majority of situations.
Anyway, if anyone has seen real data from a reputable source, I'd love to see it. I can't help but think someone must have tested this out at some point before deciding to use Vinyl for swimming pool liners.