thats looks like could be part of the genetics's with the possibility of a minor PH swing in your medium (end of your leaves are twisting as well, good sing of PH being slightly off in the medium...nothing to panic about). With the lights being so far away I'm reluctant to call this heat curl (if you was with in 10" then yes) this I why I think this is more genetics's than heat stress... you will get leaf curl when the leaf surface temp raise to high and your environment has be very warm (30c +) or the plants far to be too close to the light for that to happen... I get leaf curl on some plants at about 29c +, some will curl at around 27c but normally because they have got way to close to the light at about 5" and leaf surface temputre has rocketd bing to close to the light.
Buy an infared / laser gun thermometer of amazon (they are cheap, I payed under £10 for mine) you can then find out leaf surface temps and determine if you temps are too high
when i was growing with Burple (Mars) 15" - 12" every time in flower with Auto's... I wouldn't trust what the manufacture say's on those lights. Being Chinese brands the figure's would have been fudged to suit the marketing... they is no way that 1000w is putting out a 1000w of light, at a guess 600w if your lucky
when you move your lights closer do it slowly, half inch a day. You can then give the plants time to adjust and also keep an eye on them to see if they show any sign of stress.
your temps are in the perfect average range
