diagnosis please!!

whats wrong with my baby?have included pics, anyone know this?
im using R.O water ionic nutes,water temp 20c, tent temp 26c,humidity low 20%,ph hovers about 5.8 - 6.8 has been the worst,E.C of 2.2 . the other plants did show signs of it but seemed to disappear.

anyone?

somebody must of had this before!!!!!!!

Using the hps, while takin pics, doesnt help. Heat stress??

Could possibly be too low of humidity... maybe... if your in veg, spritz them with a spray bottle, maybe they'll relax.

hmm how much water are they getting? could be root rot, if too much.

thx for responses,
they are getting watered for 5 mins every hour,roots are already in the tank, i put them on to flower 2 days ago,its only the one plant. is it possible to still get heat stress when the temps are ok? doing my head in now!!!!!!!!!!

R the roots nice and white? No slime? Although the room might have perfect temps, hows the temp under the light? Are your leaves warm/hot?

Looks unusual like something I haven't dealt with. Check the undersides of the leaves for eggs or webs. I think it could be some kind of critters

its one of two things .....1...magnesium build up of to low humidity ....i would change water and nutes

hi guys, well the roots are dark in places, ive always had dark areas on roots before but have never suffered this before,the leaves are not hot ican touch the cooltube with the back of my hand and its not too hot.
interested in the magnesium build up can you tell me what and why about it? humidity is all i can think of thats not good.