Curious Im sorry but I cannot help you with your ph question because I do not know how to accomplish that in soil. If you want to change the ph of your WATER that you water them with this is how....but I am not sure if it is the water or the soil itself that needs to be exact.

To raise ph in water use baking soda (I would NOT put baking soda in your soil curious!)

To lower ph you can use distilled white vinegar....again not something I would add to the soil itself.