I have a 4 year old liner in an above ground pool. A blackish stain has appeared above the water line around at least 3/4 of the pool. Under the water line the liner looks good. We have had pool company come out and try to remove and we have tried several chemicals and scrubbing to remove it. But it will not budge. My question is can I use an acrylic pool paint to paint over stain above water line? If so what paint would u recommend? The liner should not need replacing yet, but it is embarrassing to have people over and the first thing they see is that nasty ring. Help!!!