My first instinct is that it is definitely the fertilizer, those plants are young enough they should be totally fine with just the ferts that are naturally in the happy frog soil, no need to add more, and especially no need to add big bloom yet. You usually don't need to start adding fertilizer until at least 1-2 months in, at least in my experience (and more like 3 months if you're using something like Ocean Forest or Vermifire), and if you are fertilizing the soil prior to planting only do it in the bottom 1/3rd of the container so the plant has at least a little bit of time before the roots reach it. There is literally zero chance that it is burning from the lights, CFLs will only burn your leaves if they are physically touching the coils, even like 2 inches of distance is enough to prevent it (And really you want the lights about as close as you can get without touching the plants, the closer the better).