Sometimes one just grows faster than the others. I wish I could help you out with nutes and whatnot. I'm on my first grow (thanks for stopping by), and I used MG potting soil w/ nutes in it; so I'm the last guy you'd want advising you on nutes.
I can tell you that you should add nutes to your water and then pH it. The pH your water should be depends on the pH of your soil. If you don't know the pH of your soil, you should pH your water to about 6.5. Your plants look pretty good for the low nute levels. Those things are about to shoot up if they are provided proper nutes, light, and water. You should do a search for what nutes to use. I wish I could help more, but I've been growing for exactly 42 days, and am far from an authority on the subject.
Good luck buddy.