All the best to your cleaning business. (It's been 6 years, if it's still going strong then good job!)
I'd like to recommend this rule of thumb for your when cleaning anything:
Acids and Bases.
For inorganic stains (mineral deposits, scales and soap scum), I'd advise you use acid cleaners which will do the trick.
For organic stains (food stains, molds, grease or anything else which came from something that is or was alive), use basic or alkaline cleaners.
For combination ones (rust with molds or something like that), use both cleaners but try the alkaline or basic first before the acids since the latter is very abrasive and can corrode your surfaces.
Anyways cheers to you and hoping for the best on your business!