Earlier quoted context omitted.
I was curious, and found the ingredients for a 1992 bar of zest from an eBay photo. It was a mix of soap with the detergent sodium cocoglyceryl ether sulfonate. The current recipe is all soap but they added a couple of chelating agents: Pentasodium Pentetate, and Tetrasodium Etidronate. The problem with the new recipe is these chelating agents suck. The only thing that can jail Mg/Ca2+ faster than soap scum forms is…
Where do you buy the STP?
https://www.amazon.com/Sodium-Tripolyphosphate-Super-Cleans-...
I did some research and it has benefits from as little a 2%, and the top performers use 35%. Not only does it chelate hard water, it effectively turns any oil on your dishes into soap.