The best thing for you to do, is mix up a fresh batch of ProMix Mycorrhizae HP + worm castings, maybe a dash of bat guano, then transplant that nute burnt seedling with some warm pH'd water...I'd feed it just water and lightly spray it. If you have a heated dome set-up, it wouldn't hurt to keep them in there at 77 to 79 degrees F too. They're sensitive little babies at this point. It's well worth the effort to baby the shit out them especially when they are babies and in the winter time. I've found no problems getting seeds to pop in the summer time or even late spring time, but in the fall or winter is another story...it's almost like they know it's winter and there's no way they're coming out in this nastiness winter time. Almost. lol