You're astonishingly detailed in your thinking on this subject AD, compared to me that is.
I'm sure that I seem silly for not having used tap water directly to replenish after a water change. My issue was that my oldest fish, and now two of his tank mates, show stress quickly and glaringly. It isn't easy to see fish this orange suddenly explode in deep black streaks. Based on what I've been reading and hearing my Python, used properly, will make for larger and more productive water changes.
Based on your insights we're going to try Prime. Secondarily, a big WC
will allow a test of my new heater too!