Problem with my garden grow (Seedsman's Velvet Bud :D)

Hey everyone, I got my 5 pack of seeds of Feminised Velvet bud about a month ago and my two babies have been doing great up until about a week ago.

I noticed slight yellowing and a bit of brown on the bottom two leaves of one of the plants and since then it has gotten slightly worse. I've also noticed it on another leaf on that plant and a bit on the other plant. They are both in the same soil and I've watered them equally - but the problem is much more aparent on one of the plants...which doesn't make sense to me!

But first thing is identifying what the problem is, so I'm calling upon all the other (much wiserkiss-ass) growers for a helping hand .

Any help is really appreciated as this is my first grow, and I'd love it to work!

P.S. Pictures are downloading to my computer now and will be uploaded as soon as they're done! Thanks!!!

Here's the pictures - they weren't as clear as I hoped they would be but it's better than nothing!!!

Cheers, Greenfingers