First Grow...

Hey everyone....i started my first grow, a little over a month ago.....they are growing pretty well with the exception of a few things...about a week and a half ago, some of the lower leaves on my plants started to look a little unhealthy...yellowish color, spotty, curling...i have a book on growing and i have looked at tons of websites...and have come to the conclusion that the problem could be a number of different things...i have added some pictures so if you can help me out in telling me what you think is going on it would be great...thanks

What is YOUR thought on what it is?

Here is a good troubleshooting guide to start with.
Revised: The Complete Guide To Sick Plants,pH and Pest Troubles - PlanetGanja.com

GET THAT GIRL SOME NITROGEN!!
Go for the fish emulsion...