When you are having to drain and backwash a lot, a sock would be better, to keep you from losing it.

A better solution for you may be to buy dichlor at Sams Club. They have a 24# pack and a 50# bucket for very good prices. Each pound of dichlor will add about 3 ppm chlorine, and about 2.5 ppm of CYA . . . and it dissolves almost instantly.