Blink you got defs going on there...Despite runnoff ph I would wonder if your plants are having an issue....you may want to consider flushing. I would consider 1/2 strength pro grow a pretty good amount of nute (imo) and you are using tap water.....you should not need CalMag unless you have some really funky tapwater. I'm wondering if you've got buildup in your soil that is blocking some nutes from getting through. I've been fighting just this sort of thing in my hdro grow recently.

Your plants aren't rootbound are they?

Revised: The Complete Guide To Sick Plants,pH and Pest Troubles - PlanetGanja.com
Plant Physiology Online: Symptoms of Deficiency In Essential Minerals

Two very good links. It would be a good thing if someone who actually grows in soil would agree with this since I only grow hydro.