I've got hard water too. As one shop said to me, you need a hard hat to take a shower. lol
Petsmart tested it, it's at 150, all I know is it leaves deposits.
Figured you were the kind of person who would tackle a problem until it's resolved.
There was another thread that suggested lemon juice. I know it's acidy, don't know it it's better than vinegar, I haven't tried it myself.
I have done allot of reading myself and apparently not even muriatic acid which is so strong it can damage your lungs, but will not take off embedded water stains overnight. In the final analysis when its bad only mechanical cleaning will do the job either by hand or machine. So its off to buy a buffer wheel for my portable drill and some glass polishing compound. Hopefully thousands of RPMs (Revolutions per minute) with the drill gun will duplicate days of hand rubbing in just a few minutes..Will post the outcome.
"dilution is the answer to pollution" .