Should I flush and harvest earlier ?

I think its because of Fe or Zn, or both. Ur CalMag fert does have some amount of iron, zinc? In my opinion, its worth of trying some microelement booster, which is commonly made for issues with overfeeding. I guess most of good fertz gets some microelem. and there shouldnt be any problem if dosing properly. But once u made something wrong, there is solution by completing micro- needs. If u dont, it goes worse. I would recommend to try micro- complex booster. Small bottle its not expensive, and gives u a lot of help when needed.