I added 1/4 the amounts of nutes specified to a gallon of distilled water and would spray about three solid squirts around the roots of the seedling every other night before the night cycle. I just noticed the yellowing yesterday.
That plant looks wayy to young to be giving it nutrients.

The first two embryotic leaves you'll see (the round ones, the very first ones that brought the plant from dirt to light) are called cotyledons, aka; seed leaves.

These little guys give your plant enough nutrients up until AT LEAST 2 weeks above soil. (this is why a seedling will grow without light if left in the dark for a few days) Also keep in mind the seed provides quite a few nutrients for the early stages in life.

What were the N-P-K ratio of the nutes you used? How much EXACTLY is 1/4 to a gallon? (1/4 tsp? 1/2 tsp?) ect.

And you're right, CFLs that close aren't a heat issue so you can mark that off of your checklist.

Btw, I'm jealous of your camera.