Lowryder yellow leaves

hello,
I'm a relatively new grower and ive been experimenting with the lowryder #2's. They're in their third week and the fan leaves have begun to turn yellow and droop down. Also, the leaves next in line up are beginning to show a yellow tint to them as well. Do you think it could be a nitrogen def alraedy? I'm using organic soil with perlite and the temp inside the box is roughly 77. The ph is less than 7, around 6.7. Also, i water every third day so i kno its not overwatering. Any thoughts?????:rastasmoke: