OK... 1 LEVELED Cup is 2 1/4 ounces..... so 4 Cups would be 9 oz.... I used half that amount for my smaller filter...I slurried with approx 1 gallon of water and slowly poured in..... Again, i based my decision to backwash, by the outflow at the return..... i am backwashing every few hours...probably dont need to do it that often, but I do like the results im getting....