So just to recap Darrel. Could we conclude that "pH drop" is independent of KH? Even if its not exactly 1 unit of ph. In other words you need the same pH drop no matter the hardness of the water. Now there are also other acids/bases. And this is another big question. Is it still the same pH drop if we add an acid that? I think it is because it will break down KH. And is it the same pH drop if we add a base? Dont know.
Actually this is quite easy to test and Im testing it indirectly now in my tank. Im adding H3PO4 to lower pH whilst maintaining the same BPS and difussion method. Ill find out today if the pH drop stays approx the same. Yes I know this isnt scientific but its something.