I never indicated nor posted that pouring pH'd water through PM media or other soil-media would significantly change the soil pH.
I just said you need to test & pH your water and soil before using and along the way.
That is not the purpose of pH'ing the water (changing soil pH). Ph'ing...
Do you even test Pro Mix (PM) for media pH? According to the PM mfg website (doing the reading for you here Regrowth here):
PM is “packaged with relatively low moisture, so the limestone does not activate for some time; therefore, freshly packaged growing media may have a pH of 4.5-4.9...