I have a 18 by 33 above ground pool. I have grainy grayish dust that appears on the floor. It started at the end of last swimming season. I kept putting chemicals in the vacuuming and it would return. I closed pool giving a very thorough clean. I just opened pool back up 6 days ago and the dust has re appeared. I have ran out of ideas of what it is and how to make it go away and stay away. It is very frustrating. Please help!!!