Runoff pH.......

Get yourself a good amount of tap water, check the pH of that water then add a bunch to it so that it is running out the bottom of the pot. Capture that water and test the pH again. Now you have the pH of the water before it hits the dirt and the pH of the water after it comes out. The pH of the water that has been thru the pot is the pH that you want to be around 6.5 - 6.9. The soil may pH at 7.0 BUT can have peat or other things in there to bring it up, or if you have nutes in the water will bring that pH WAY down..... I think you will see the problem with you do a soil run-off pH test.