How much detergent should I use depending on my water hardness?

For soft to medium water (0–6 grains per gallon) with normally soiled loads, fill the Main Wash section to the top of the 2nd step (2 tbs or 30 g). For medium to hard water (7–12 grains per gallon), fill the Main Wash section to the top of the 3rd step (3 tbs or 45 g). Never use less than 1 tablespoon (15 g) per load, and always use automatic dishwashing detergent only. (Page 12)