Sorry, I'm not a hydro guy.

Just a guess...but possibly too high ph, and slight overnute...?
What's your nutrient schedule?
Temp swing is marginal. If possible, keep within about 15 degrees f. high/low. The wider the swing, the more it can stress the ladies.
Do you use any other additives, sprays, goops or gels? (micronutes, CalMag Plus, Liquid Light...)

Again, I'm a soil guy, but answering these may help others to help you.

Good luck.

Edit:
I just saw your pix...and nothing looks at all drastic. Matter of fact...they look pretty good so far. :thumbsup:
Rusty Trichome Reviewed by Rusty Trichome on . HELP... Yellow Leaf Edges! Potassium deficiency? So i noticed the first signs of DRAMATIC leaf colour change yesterday on two of my Mystery Seed/Juicy G plants. My inital reaction was that the 42w CFL bulbs i am using are too close to the plants and burning the leaves, but this discolouration effect only happened on 2 of my 8 plants and of those two only one or two lower leaves were affected. To compensate i raised the lights another 4" from the plants, but when i returned today the yellowing edges have carried to another set of lower Rating: 5