Bruce:
Soap scum and mineral deposits are two different things, so a bathroom cleaner for soap scum isn't going to do much good (a few bathroom cleaners do have the ability to attack mineral deposits, so one of those might help; read labels carefully).
The best thing for mineral deposits is Lime-A-Way, but it can attack porcelain if its acid is not neutralised and rinsed away promptly. Test Lime-A-Way on an inconspicuous spot, and if you do not observe any etching or colour change, use it according to label directions, following up with a solution of baking soda and water to neutralise, then a very thorough rinse.