I noticed some grey stains on my vinyl liner after removing the solar cover. We have had a lot of rain and cool weather in the Northeast, so I haven't been in the pool much this year. The cover was on for a few weeks, and I didn't check much underneath it.
When I finally pulled the cover off, there was some algae (not much), and these grey stains. Chlorine level was 0, and pH was 6.8. I raised both to normal, and cleaned the pool. Everything looks great, but there are still stains on the liner. I can't scrub them off with a brush or my hands.