@BartButenaers - I don't know if its even possible to measure the salt content post treatment; its just a thought but more research would definitely be needed. I think the salt content in softened water is quite low, and you might have to compare it to the level in the pre-treated water then look for a difference. Seems to me that if there are sensors capable of doing this, then as prevalent as water softeners are, the sensors would be readily available and marketed for such use.
Regarding pH & hardness, I believe that for water softener systems to work effectively the water must be within a certain pH range. If outside that pH range, then the pH as to be treated before the hardness can be treated. That may be the source of the confusion.
Terry Love Plumbing Advice & Remodel DIY & Professional Forum is a great site for these matters. Another might be pool/spa treatment, since they often use salt to generate chlorine. TroubleFreePool.com has a lot of info and forums that might be worth reviewing.
