What could be wrong with my plant???

It started off as a an experiment just to see if i could really grow so i didnt put ne money into special lights or nutes, although its been growing very well till a few days ago. The tips and outline of the leaves started to get a rust color and 2 died! what could this be?
7 weeks old, cfl light, just schultz potting soil no nutes or fertilizer! could this be the problem?
ANY HELP IS APPRECIATED! THX

I'd say it's ready for some nutes. Not sure what you're going to use, but I'd start out at around half strength and work up.

what nutes would u recommend and how should i set the feedung schedule?

Well I use GH maxibloom, that's it. I'm also growing in hempy's so I feed every time, but in soil I'd probably Feed, water ,water feed. You can play around a little with that too. If your plants are heavy feeders you can feed more often. Mix your nutes, adjust your pH if you need too and you should be ok.

thats it just needs a lil food I would even start with 1/4 of what the directions say just to be safe anything with strong nitro or just some seaweed stuff all of the options out there work

My best guess would be potassium deficiency. It is hard to tell from the pictures

Potassium deficient plants have leafs that start to die along the edges . The leaf will eventually turn yellow and die.