Nutrient lockup, ph out of balance. Don't feed them yet, your soil looks like it's good soil(has a lot of nutrients in it from the start) so there's no need to feed for a long time(first 3-4 weeks in veg). I'm sure even on your bag of soil it says to not feed for the first month or so, unless you have really shitty soil.
Also you have CFL's which doesn't provide that much light compared to HPS and thus plants grow slower and use less nutrients.
Just give them ph balanced(6.5) water for next 2-3 weeks.