I couldn't decide which Category to post this in, but I'm guessing it has something to do with water chemistry. I've noticed that the fiberglass shell feels somewhat textured or "dirty" everywhere that's underwater. Above the waterline feels smooth like glass. It doesn't feel like sandpaper, but more like a dirty car that needs a carwash. The water is crystal clear. As far as I know, all my numbers are where they need to be. I've tried to clean it with a green scotch brite pad and it doesn't seem to have any effect on it. Any thoughts on what this could be?