White widow/ ssh grow 2 weeks need help plz

Hey guys I am in need of some help. I have 21 plants (6 ssh, 15 ww) and some of the plants lower leaves have yellow coloring on them while the top leaves are curling inwards, any thoughts? Also like 1 or 2 are a really light green in color not as green as they should be. I know their are alot of posts and stocked about plant problems but their are so many with yellow coloring I can't figure out the problem, my guess is nute burn but I could be wrong, I'm doing a flush ATM hopefully it will help I will try to upload pictures later from my comp.