What you need will vary from area to area. The type of minerals in local water, the soaps being used by your customers, the amount of deposits... all variables. No magic bullet.
One way to think of it is that you are breaking down a layered
matrix, so rock the PH back and forth until it is done. Friction is your friend, so an orbital sander, a Makita or whatever with a red pad to avoid abrasive scratches. Sometimes a plastic scraper. Harbor Freight sells red plastic chisels that you can resharpen with a pocket knife. Get a set.
If you find a really good alkaline for your area and a really good acid like Barkeepers Friend, stick with them.
Avoid Viper Renew in bathrooms. It is choking and turns chrome blue. It rusts hell out of stainless.
Experiment!