New growth is light green? (1st grow)

New growth will be a bit lighter before it can darken up. Normally nitrogen will show on lower leaves first and Iron and Sulphur issues will show on the top new growth with symptoms similar to this. However it maybe in the soil but just not available because of the PH. I tend to grow in soil at 6.4, 6.7 is on the higher side of my preference, and if growing in soil the PH can swing from microbes. If you get runoff, test its PH, if not try and make a slurry of the soil and distilled water then test that water after letting it sit for 12hrs. I have a feeling this is caused by PH but it should be a easy fix. ....[][][].... Also regarding your lights. if they are on more then 18/6 that can cause issues, plants need downtime and not having it is bad for them. Fix this before messing aorund with anything else if they are on a schedule that's greater then 18hrs on. ....[][][].... Good Luck!