Hi Dave, good to see you are becoming so knowledgeable on the little waffle glass cloths, yes they will not remove the efflorescence from the glass, but we can offer you a product that will remove it safely from the glass as this product contains no hydrochloric acid, it comes in a 1ltr concentrate bottle which you can dilute 3 to 1 into a trigger spray bottle then apply it to your glass surface spraying the solution from the bottom up to the top, then let the solution dwell on the surface for 2 to 3 minutes, then finish off by using a damp magic eraser pad to remove the ingrained efflorescence, sometimes if the efflorescence has been on the glass for long periods of time it can etch itself onto the surface making it almost impossible to remove. but in your situation as you are cleaning your clients windows on a regular basis this method should work very well. Regards Tadgh