Off the top it looks like heat stress.....but you stated only one plant has the issue (not the one closest to the light is it?). I'd check your ph runoff and see if it is in the proper range for soil. Also could be a bit of overnute......hard to say.....so check everything.

Also not sure about your water source ph......if you are watering with anything outside the range of 6.2-6.8 I'd certainly stop doing it and make sure you water within those ranges.
Weedhound Reviewed by Weedhound on . What Is Happening?!? Sup guys, So these are 2 NLxBB from nirvana seeds(:buzz_saw:) and they have been growing........well. They are 19 days old and my temps are fine (75-78 day/61-68 night) humidity ranges 30-32%, ventilation is cue and all is well in the room. On the other hand, on the plants leaves the edges curl upward like they are folding in and idk what it is. Ive considered multiple problems like temp to humidity ratio, heat stress, and added nutrients in the perlite i used etc.. The thing of it is that Rating: 5