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

For the POTSCRUBBER cycle with soft water (0–3 grains), use a half-full main cup plus half-full open cup; with hard water (7–12 grains), use a completely full main cup plus completely full open cup. A filled main cup holds 3 tablespoons and a filled open cup holds 2 tablespoons. If your water exceeds 12 grains of hardness, a water softener is recommended, as lime can build up in the water valve and may cause flooding. (Page 7)