What wrong with her?

After looking though the last 4 or 5 weeks, i think we have ourselves an honest to goodness magnesium deficiency.... interveinal chlorosis and rusty spots starting to form on mid plant leaves. You only fed at ~630ppm and couldn't have been oo far above that in any recent week, if not whole grow. epsom salt or cal mag. how much depends on how much is in what you regularly feed. The other pictures give a much clearer view. It's early stages and looks way worse under your grow light than it is. get Mg ppm up around 80 and S-100+, Ca - 100ish. this wil depend upon the water you use... e.g. i have fairly hard water, so you may need more. n/p/k - 120s/50s/190s will do you good