Thats a K (Likely) or Mn deficiency.....flush your plants then give them what they need, try a PH of around 6.2. Foliar sprays are great for correcting stuff like that real quick.
Cyclonite Reviewed by Cyclonite on . Sick plants, black leaves curlinng etc, overwater? I cant' figure out what the problem is, I've got 5 plants I just switched to flowering about 2 weeks ago, 3 are looking great and budding nicely, 1 has been dieing and not budding, and the other one is on that same path, spreading these Black marks all over the leaves, and then they turn yellow and curl up and are cruncy/die and i have to pull them off.. It spreads from the bottom leaves and gets all the way to the top leaves, only the newest growths are green, but the 2nd to newest growths are Rating: 5