leaf problems, curling up/discolored!

600watt HPS hortilux , 5 gallon fox farm ocean forest soil, critical kush , adavnced nutrients fertilizers. very curious as what to may be causing my leaf problems around 2 weeks into flower and over the last 48 hours, the leaves on one of the plants has done this, curling up , brittle and discolored. I just flushed the soil after seeing them like this, any input would be appreciated.

HMMM...just my opinion...but if I saw this on my gurlz I would likely start here:

http://www.growweedeasy.com/magnesium-deficiency-cannabis

I wouldn't of worry about that little curl the ppm may been a little too high but nothing to sweat about~

they were starting to droop, you watered. damage done appears so. move on...