This looks like Lack of Oxygen and excess salts at the root zone and it will make your leaves thicker Hence the curling down. It also depends on drainage and such or oxygen levels in Hydro .. But some strains are hypersensitive and will throw the same fit with excess nitrogen ..Usually Land Race Sativa's and there offspring will display such but I dont see that above as I notice excess leaf tissue and salt builup ........ What you can google under cannabis is leaf clawing . There are hundreds of images and write-ups
I hate people who ask for help and just give pics.. what medium or method are you growing? Nutes? PPm? PH? Soil? etc.. I mean we can make a wild guess but most of the time that is what it will be with the information missing just a wild guess.