Whats happening to my ak47, anyone?

Hi 5 weeks veg just thrown into 12/12 using cana veg & bloom nutes, i have noticed the leafs are yellowing at the edges working its way up the plants, any idea whats happening?

nice looking bud purp in back there by the way. i dunno though, at first glance i said nitrogen deff. but as i look closer im thinking a lack of sulfur. what kind of soil you have?what happens is the vein remains green abd leaf stems and petioles turn purple. leaf tips will burn or curve downward. if its pretty much on the newest growth, i believe thats what this case is about. i would flush with clearex first then start my nutrients over because this happens if there is an excess of salt or to much calcium present.