Bingo---in the swim black algaecide treatment 11.4% copper sulfate pentahydrate. So will this mean also metal staining as I dont see any?

I have been fighting for a few years what appears to be black algae stains at various places on the bottom . I think it is coming from the underside of the liner per everything I have researched. We have had a extremely wet summer in Pa and without a doubt have water under the liner and this is when it always appear. If I treat with shock it will lighten but not completely remove and it will get darker each day .Did not appear to be present at opening in April