I remember talking about how soap and hard water form soap scum in chemistry class years ago. My sister tried making homemade laundry soap with borax, ivory/feels-naphtha, washing soda, etc. Over time her whites yellowed and towels didn’t work so great. I told her it was forming soap scum because of the soap attracting the minerals in the hard water. But, people say borax and washing soda break up soap scum. If this is true, why did it still build up? Also, many argue people with build up must be using too much. Some recommend doing a rinse cycle with vinegar. I just wanted to give a friend a heads up about the soap scum reaction and then wondered if users of this concoction are leaning in borax and washing soda to counter that, and if it’s possible in the same cycle.