Im sure your correct on the commercial P and tough to police homeowners. Perhaps costs of fertilizer for next year will curb some of it as my cost has doubled since last November.I realize many Lowes type stores will always use it as a lost leader type product but I see they too are offering P free.When I have swimming pool goals with an occasional fish thrown in I do use 191 and like it. Shallow water ponds are still my most difficult but I find turns that are one plus usually disturb planktonic algae formation,this is why you may be able to add plates if you have area or pockets that are not being effected by aeration. Knowing that it takes very litle available P to have planktonic algae I think anything you do may only be a temp solution.What type of math are you referring to on the installs