Plant problems, any ideas?

[DoobyDoobyDoo]

Okay, this is my first time really growing on a large scale and I am having a couple problems with a few of my plants. I was hoping i could gain some knowledge . Anyway I have a few pictures. I have an idea of what the problems maybe, but I don't want to act on it until I'm positive.
Check the pics, and thanks for your feed back.

The first plant here is the one im really concerned with. The leaves all look super thin and are curling.... Also all the leaves at the bottom are dying. Also, it's in veg, any ideas?

For this one, i have a few like this, they are all in veg and about 1 month old, suggestions?

Last but not least, this is the only one like it. It just has two leaves that are browning like that.

 

[Bud stankalot]

The first pic looks like a thirsty girl. How do you water and how often? What nutes are you using?

If my soil gets really dry I water with about 5-6 cups of water and let that soak in. If you water when the soil is hard and caked, all the H2O will run down the sides and not saturate the soil. After a presoak, I water with about a gallon in a 5 gallon pot to wet the soil all the way through. You should have a bit of run off to make sure the deepest part of the soil is soaked.