Have not been around here for quite awhile but I have a question. Can scaling occur in an above ground pool? A pool with a liner and not plaster, grout etc? Reason I ask is, on the bottom of my pool there is "something" that will not vacuum up, will not rub off, will not scrub off. It is sort of rough feeling and looks like what I do vacuum up but this will not come up. It goes around the whole pool with 90% being where the floor starts to curve up to the wall. Water is crystal clear. Never had this before. I am stumped.