I don't know the answer to the PH question...
I have to say that I was using Miracle gro a few years ago, and had this same problem. I use a product now that is urea free, and eliminates salt buildup, at least for me. I haven't had the problem since I switched. Except for when I use the rooting fert, (MGro quick start) I only use it once at repot, and I always see the problem come back.
What I'm using currently is Bonsai Pro by Dyna-gro. It's pretty inexpensive, it's liquid so easy, and you only use 1/4tsp per gallon. It also has micro and macro nutrients. I've also picked up some green dream for the summer, as I want to step up my fert program.