stick a ph meter in your water, now put that water into a cup of your medium and let it sit for 1 hour and dump the water out and test it again. now try it again with 4.0 or 9.0 and watch the same results.
I never said ph'ing your water was not gonna work and even work good , i am saying there is little to no value in doing that unless your food is fucked (under 4 , over 9)
Thats about the closest test your gonna get with soil and most soiless mixes. unless of course you send it to a lab.
I have been playing with soil/soiless for many years , i dont want to argue , just simply sharing what i have learned through my own learnin
wb