leaves burning/noob questions

I have some 2 1/2 week old bag seeds growing under a 400w hps light. They've been growing good so far but the past couple days the bottom leaves are turning yellowish. On a couple the leaves are starting to curl inward also.

I don't use nutes, do I need to add some? If so what kind? How big before I transplant them? Are they looking healthy for 17 days old?

Sorry for the noob questions I just want my babies to stay healthy.

is that your thermometer there in the second picture? if it is, it looks like its reading around 95 F. that's waaaay too much. get a fan in there and get some air flow going. you want your temps to be around 75-80 F and around 65-70 F at night. (give or take a few) it looks like your plants are heat stressed. hope that helps.