The answer lies in your runoff ppm- it is RISING dramatically- you need a good flush, then start feeding wiht a weak solution of your fertilizer, and give a foliar feed with a weak solution of your GH Micro for the visible deficiency. That does NOT look like a straight Mg def, so no more epsom salts- you could be adding to the problem- it would not surprise me if that is what is causing your runoff ppm to be so high.
You are aware that the GH 3-part is rally meant for hydroponic applications? I have never tried running it in soil, but suspect that you would have to flush somewhat regularly to keep on track.