One of my plants has been developing brown spots. The plant itself is almost 3 months old and is about 6ft. I've had it under 12/12 for awile with a 400w high pressure soidum lamp and the buds have developed real nicely. I started noticing the spots a couple weeks ago so I initially pruned the leaves that were affected. I thought it might be a PH problem or a difficiency of some sort so I bought a PH tester and some tiger bloom. My PH was a little high, but only about 7.0. With the Tiger Bloom added it goes down to about 6.0. I've been feeding them for a week now and the leaves have become a healthier green, but the brown spots have continued to come. I was wondering also if it was mold, but I've had the room de-humidfied for awile and the problem still exists. If anyones got any ideas it would be awesome. I'll probably be flushing the soil right after i write this so we'll see if that helps. I'll also post a picture in a few.

Ended up going out last night and forgor about the picture. I've seen all the pictures for abused plants with brown spots and I haven't seen something exactly like mine. It's not the worst effected leaf, but it should give an idea of whats going on.

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I am having the exact same problem, however my plants are only 2 weeks old..... Im reall ynot sure whats causing these spots.... hope nothing too bad comes of them

get a pic of the whole plant and some of the under and top of the better leafs

keep your heat in check. if its around 75º you're fine. if not, that's part of the problem. if heat is fine, it looks like a maganese deficiency

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one way to tell if its a magnesium def. is it will start to yellow/brown from the veins first.. then outwards... hmmm because its not the tips i would say that your watering and drainage is fine... some forms of fungus and spots can happily spread without the normal humidity, leaf spot and black spot? although the latter is normally associated with fruits etc.. have you tried using a fungicide for spots and mould though?

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I am having the same problem! I have been a grower for many years and have never had this problem before. I have fungus gnats at the moment however they are just affecting the babies not the adults. The adults have circular brown spots on yellowing leaves at top and bottom of plant. Also the adults are 2.5 wks into bud. At first I thought it might be a heat issue but I have my fans running. My ferts are the same as they have been since I started so I know that is not the problem and I do not use tap water. If anyone has any helpful ideas I am all ears!

i have found this link helps me alot!!! hope it helps!!International Cannagraphic Magazine Forums - The Complete guide to Sick Plants,pH, and Pest troubles!

did you see the pic of the manganese def. brown spots with yellowing leaves!!

none of those photos resembles the problem I am having! The spots do not seem to occur in any type of pattern, they can be in the middle or ends, the leaves don't curl just turn yellow and have brown spots. I am honestly at a loss!!!!