My plants are looking much better since I added Mg (epsom salt), but older leaves on the wisteria are having trouble, turning dark and curling downwards. Since new growth looks good, my guess is that a mobile nutrient is lacking. Since P and N look good (0.5 and 20 ppm respectively), and I am adding plenty of Mg, the only other moblile nutrient I know of that might be lacking is Zinc. Does this seem reasonable? I dose Flourish (not Flourish Trace), but have read that it is low in Zinc. Am wondering if CSM+B or another source of traces might be worth trying. Thanks.