Went to the pool store and they indicated i needed to add 9lbs of baking soda. I was told that 1 lb is equal to 2 cups, so i started by adding 6 cups which should be 3 lbs (per further instruction to break into 3 incremental doses). I am now thinking that the cup felt pretty heavy and am wondering if 2 cups is indeed 1 lb? I am fearful that I used too much and will overshoot which I am now reading would be an issue. TIA!