But you won't know what your final PH is. I'm no soil grower, but I was under the impression you check input PH as well as runoff PH.
Let's say your optimal PH is 6.5-7.0. So if your input PH is 6.5 and your runoff is at 5.1 you need to adjust your PH at next watering higher so you can also increase runoff PH. This should be gradual. So don't go adding 10.0 PH water. You would keep adjusting your input PH to around 8.0-8.5 I'm guessing until your runoff stabilizes. Please, someone, correct me if I'm wrong here.