I have an indoor dwc set up, use gh flora duo with cal-mag and hydro guard. I can't seem to get a hold on this brown spot problem. I added more cal mag thinking it was a mag deficentcy but still have leaves comming down with it. I came across a picture that looked a lot like my fan leaves and it was "leaf septoria" but it supposedly is an outdoor grow fungus.
(Mg) def. is an 'old' plant issue like arthritis in humans ..lol this is early to mid nute burn, flush well no nutes until you see an active recovery to my blog: http://forum.grasscity.com/blog/1093/entry-9829-flush-baby-flush/
Thanx Ancient Member, just changed res before i read your reply. gonna put 4 or 5 more gallons of water in to cut ppm down. Was running about 875 ppm but set this one at 650 ppm. 5 more gallons of ph'ed water should bring that down. will let you know