I had a vinyl liner replace 3 years ago and every year since then every time I open My pool I have brown organic stains all over the bottom of the vinyl liner. I assume these are from the worms that accumulate over the winter. They leave their impressions on the bottom. Is there anybody out there know how to get rid of these stains. Theses stains go away over the course of the summer either from the sun or chlorine bleaching them. By the time their gone it's time to close the pool.