Dito on that Bob. There's also Softener Mate, ResCare, Citric Acid, etc.. These chemicals are dessigned to work with the resin inside the tank, so put the riser in, put the gravel in, put the resin in, and screw the valve on. Conect the valve and salt tank. Follow the directions on the chem's Instruction Panel. You should see the fouling drain during the Backwash and Rinse cycles. If it doesn't recover you'll new resin, probably a specialty resin like fine mesh, etc. combined with a continous chem treatment or pre-treatment.

On a 9" tank 1 cu.ft. should fill the tank a bit over 3/4 high when you add a 6" support bed.