You have to add CYA--WalMart, Home Depot, Lowe's, etc. sell it--it's often labeled as balancer or conditioner....but if you look at the ingredient label, cyanuric or isocyanuric acid is what you want. Follow label directions to raise your pool up to 30, but don't broadcast it---instead, put it in a sock or knee hi hose and put it in the skimmer or hang in front of the return...or slowly pour it into the skimmer with the pump running and don't backwash it for about a week.

Janet