Ron:
Are you using water that has been treated by a domestic/home water softener or is it a (untreated) municipal-sourced water supply?
If it is straight tap water (AKA, untreated municipal-sourced or ground well water, how "hard" (IE, mineralized) is it??
I NEVER wash in the sun here in Green Bay WI as our municipal water source is Lake Michigan and has a "higher" amount of calcium/limestone in it, not to mention the chlorine they add to it in the summer to disinfect it from E-coli-induced farm-manure and municipal waste treatment plant runoff. It is a royal disaster if I do wash in the sun and using a hard-water mineral remover after a vehicle wash seems like an extra step and expense, albeit necessary.
Never found a soap that "conditions" hard water, even though Optimum`s No-Rinse is "suppose" to do that. Then again, never used OTC-purchased distilled water jugs, as $5.00 for the 5-gallons of water to be used seemed, well, "non-economical" to me (Yes, I am "thrifty", AKA Cheap!).
Now if there is a car washing soap that CAN be used in the sun WITH hard water, I need to know about it.
Otherwise, it`s car/vehicle washing in the cool and shade of the early morning or late evening via a 2-bucket method and municipal-sourced hard water .
Oh, yah, let us know about that secret "test stuff" on the hood as soon as you can. Hope it is a product that revolutionizes (or at least, enhances) vehicle appearance.