Root problem?

Judging by both leaf curling and dark green leaves, points to nitrogen toxicity. Lay off of any feed with nitrogen, you shouldn't need to feed them anything with nitrogen after switching to flowering. They need plenty of potassium and phosphorus when in flowering stages. Let the plant use the nitrogen stored in its' leaves for the remaining of the grow.

hi buddy..... not a root problem to my point of view bcause all the plant should show more symptoms..... i can recommend to you next time to be a little more précise....bcause we don't have a diarie to refer to your nute schedule for example...or your grow's environment so it s hard to be fully affirmative same for your first pics....extremely hard to correctly see with that light.... better infos/pics you can give...better can be a diagnosis 👍 keep that in mind 😏 dark color seems to be is a light N overfertilization but nothing really bad i think is all plants are affected or not ?? do they look like that? https://www.growweedeasy.com/wp-content/uploads/2017/02/wind-burn.jpg here next stage = https://www.growweedeasy.com/wp-content/uploads/2017/02/wind-burned-leaves-clawing.jpg how many fans do you have...and how powerful they are ? even with good temps you can burn leaves with too much wind/fans....ithey can act like a drying machine....if in addition your temperatures are a little high u have your diagnosis....reduce wind...spray with bio vera or something like that...as u seem at first stage everything should get back to normal quickly. again i can't be 100% sure...but i hope this could help you ! happy growing