Hey man, as long as its just the bottom leaves, I wouldn't sweat it too hard. If it starts spreading all over the plant, you might have a problem though. Overall, the girls are looking spectacular. This past saturday was the end of week 5 flowering for me, so I'm just a couple days ahead of you. These last 3 weeks is where it gets really exciting, at least from what I read thats when they pack on the weight.

http://www.drugs-forum.com/growfaq/97.htm

That link is to the "Plant Abuse Chart" which is a great too for diagnosing plant problems. It has pictures of leaves from plants that are having too little/too much nutrients, what is wrong with them, and how to correct it. Bookmark it, it comes in handy :jointsmile: