please help w/ diagnostics

Can someone confirm this is nitrogen burn? I repotted w maybe 40% perlite. (the rest FF OF). here's image: http://ibb.co/hXBRDa

Here's image of a seedling I'm having troubles w also. What the heck?
http://ibb.co/k7HSKF

I'm new. W/ seedlings, they're under 750w Mars Hydro LED during the night and outside during the day.