How much detergent should I use, and does water hardness matter?

The amount of detergent depends on how soiled the load is and the hardness of your water. For soft to medium water (0–6 grains per U.S. gallon), use less detergent; for medium to hard water (7–12 grains per U.S. gallon), use more. Using too little detergent in hard water will result in unclean dishes, while too much in soft water can cause glassware to etch. (Page 4)