STPP usage with hard water
I need advice on how to use STPP under my local conditions. The water is rated 11gpg (191 ppm), I have a new Bosch 500 frontloader, and am using Sears HE free & clear detergent powder. We have 3 children in our house, including an infant, so I tend to add extra rinses to my washloads.
I am planning on starting with 1 tbls of STPP to 2 tbls of detergents. However, my bigger question to ask is this: do I need to do anything to the rinse water besides adding fabric softener? My towels and clothes currently come out very stiff. I'm worried that they will continue to be stiff due to the hardness of rinse water. It doesn't seem like STPP in the rinse water would help.
I appreciate everyone's advice on this in advance.