I am having this same problem in the flowering cycle also. I can tell you that it did not happen because of a change it light cycle though which im sure you know but mine started turning brown on my fan leaves about 3 days before i switched to the 12/12 so I know its not that. This is my first grow that ive done with Canni but ive done some pretty amazing things with veggies like cross breeding a strawberry plant and cayan peppers but this is a whole new set of probs. I dont have the ph kit (yes i know I need one but I am disabled and havnt worked for 3 years so i dont have the money) Ive got a website that I know of that might help you. Ill link it up here for ya. Its got pics of all, well most of the probs that these plants go through. If I remember correctly the closest pic that looks like my prob is low Mg. Do you have anyway of testing that? Some people say that low mag can be fixed with epsom salt in the h2o but some are very against it so I guess thats up to you to decide on. If you figure it out, post it up here please id like to know before its ruined.
My canni is a Mango, she is a sensi clone, 16in now and was moved into 12/12 5 days ago. It may not be related but take a good look in the soil and around the area for little worms. Ive found a couple of them in my res tank and the soil but nobody seems to know what they are. Ill attach a pic too.
Marijuana Plants Problems - Yellow Leaves, brown spots, nutrient shortage etc.




Quote Originally Posted by greenthmb
Hello everyone! This is my second closet grow, and after a successful first grow I am stoked to harvest again. I have 6 plants in Fox Farm soil, under a 400w hps, light at 12/12, circulation fan, temp stays between 72-76 degrees, humidity stays around 40%, watered with Nestle Pure H20 (which is supposed to be a pH of 5.5), and they are fed Tiger Bloom, and Big Bloom Fox Farm nutes every other watering (once/wk).

All of the plants are big, green and healthy except for one, Wild Purple, which is turning a light green/yellow color and has developed brown spots on the fan leafs, and some of the top leaves. The buds that are forming are beautiful, and the plant doesn't appear to be croaking.. but I simply don't know what the brown spots are, and don't want to let it get any worse. I've checked for spider mites/pests/bugs- none. I do feed a lighter dose of nutes, because I tend to err on the side of caution. I checked the soil pH today and it was 7.0, which I know is slightly high.

Any advice would be appreciated. I'm leaning on feeding it some Cal-Mag to see if it's a Mg deficiency, but it is such a beautiful plant, I really don't want to use it as my test subject. Thanks in advance, and sorry about the crappy pics!!!!

Happy Growing :jointsmile:

Attachment 272905Attachment 272906