What would be causing this?

I have a indoor setup(ebb & flow). The girls are in 6" rockwool cubes. I am now in week 3 of veg. They are watered once daily for 15 minutes, 15 minutes after lights on. Ph is at 5.8. So check out my pix. There seems to be some browning, and the edge of the leaves are curling upward.

Im pretty sure its not the heat, the lights are high enough to not heat my hand to much.
All help is appreciated.

So it would seem knowbody knows. lol.
I think now that it might be a Mg def that I am currently trying to fix with a product called Amped or something like that. Since Ive started spraying them with it, seems that the leaving are getting greener and the edges of them are not curling.. as much.
If anybody else has any other ideas please let me know.

greetings bionicron im new here but check this pagehttp://http://www.cannabis.com/growing/plant_trouble-nutrient-profiles-and-deficiencies.html good growing to ya