RT is right about air flow.
The cause of that symptom is a high heat and a low humidity. Bring the heat down to ideally 78'F and the humidity to 30-40% RH, and the edge curl should go away.
The plants look healthy overall. Should be a simple fix.
stinkyattic Reviewed by stinkyattic on . Leaf Curl - Over watering?? I've posted some pics of my cheese planted which is in day 26 of flower now. This is my 3rd closet grow but first under a decent light. 1.5m h x .75m w x .4m d 600w hps John Innes No.3 mixed with pearlite Feeding Hesi Bloom & Top Maxx every other feed. Temp at top of plant 86C Light is .4m from top of plant Rating: 5