We seem to have hardened algae(green) around the bottom edges of the liner. I have brushed it over and over and it just doesn't come loose. I rubbed it with my foot and it feels hardened..like rough and like it calcified to the liner? Can that happen if you don't brush it when it forms? We were lazy with the pool this summer since no one was really using it. The water is clear, I just can't scrub the algae off.