Got the same thing happening with my grow, i thought it was a Nitrogen deficency. I have added a 18-18-18 fert to them about 4 days ago, havent seen any improvement yet. Let me know if you get to the bottom of it
My first grow is underway in a grow box and when adjusting the lights a support fell and broke off about 4 fan leaves and 3 other branches that were growing on the lower half of plant(plant is 18"). I am 10 days into flowering and the plant is female. I had no choice but to cut off the broken...