I agree, it needs a mild nute of some kind (not familiar with B52). Looks like Mg and maybe N deficiency. I wouldn't worry about the N yet, but a foliar with kelp will give it some Mg, Ca, and trace minerals. I use Eco-Nereo Kelp, it also has Humic acid. Don't give it intense light yet. How well established were the roots?
Edit: just looked up B52, I think that should work fine for a foliar spray, good luck.