Bottom leaves turning brown, 2 weeks old. Pics included

Earlier this week I was having an issue with my plants leaves curling up and wilting. I took care of that problem by revising my ventilation system. Anyways now one of my plants is starting to yellow up on me.. the pic will explain it all

This was yesterday


Same plant today



I thought at first it was a N def so I went ahead and gave all my plants 5ml of Grow Big mixed in with a gallon of water after I transplanted them.

Any help would be greatly appreciated

see what looks a lil like a nute deficiancy, who knows, i guess we'll have to give your baby some time, o yea good job on catching ventalation, not too many catch that in there more biggening grows.

ph? might need a cal/mag nute, my jock horror's use it like its going out of style even from seedling stage. i had similar problems.