When watering or adding supplements I never have runoff so perhaps this is part of my problem. I began saving my soil after harvests because the cost per bag is $50.00, so it kinda makes sense that I have the buildup..I am still playing around with ratios. The recipe I am trying also asks for a bump in Ca for the first 3 weeks and then a MPK bump weeks 4-6. It also depends on your environment. I'm using a blend of LED and CMH and my Mg needs are greater. With these salts, small tweaks have a large effect.