Did you recently just add DE? We added 4lbs. of DE to our skimmer when we put the pool up 3 weeks ago. I kept finding fine/white powder substance on the bottom of the pool. We would vacuum it up and then it would be back the next day. This went on for over a week but it is now finally not happening anymore. I think it was just excess DE from our initial 4lbs. we added. Maybe next year we'll only add 3.5? Good luck!