I have an inground 50,000 vinyl liner pool. Four years ago, I purchased and installed a new liner. The pool was open that year and the next, then I did not open it for the next two years due to moving out of town. This year, I began by spending hours removing leaves as it had not been covered. It was a green mess with frogs hatching out in it. I called some professionals, as it seemed too much for me. After about a week of work, the pool is clear. They just finished vacuuming the silt off of the bottom, but now I noticed there are very large, white bleach stains all over the bottom of the shallow end and on the slope going into the deep end. I don't know if they are at the bottom of the deep end as it is still a little murky there. I called the pool people, as these stains were NOT here before. They told me that they had been concerned when they saw the stains as well, but that they had not caused them as they predissolved the shock, and this was the only chemical they used that could cause this. They did tell me previously that they had used about 20 pounds of shock. My question is: could these bleach stains have been caused by the shock even if it was predissolved? If not, what could have caused this? Also, will this weaken the liner? Any feedback would be greatly appreciated, as I spent ALOT of money on this liner a few years ago.