you should be using both veg and flower nutes, if you have an advanced kit, if not idk. they take a while to mature to sex age even tho they are in 12/12, so you may have to wait till they get to be a few more inches big and deffinately a few more node lengths. they dont look too bad ill see if i can find a picture of my plants at near 20 days to compair. i didnt use any nute other than what was in the soil.
these are my 3 week (21 day) pics, i had them under 4 26w 2700k cfl bulbs. how far away is your 400w? thats what i have now but i have a mh convertion bulb in it, i have it as far away as i can get it cuz the heat, heres a page of info that might help, that might have stunted them a bit. just make sure you have a fan on them all the time. promotes fast strong growth.
http://s384.photobucket.com/albums/oo281/MrJDGaF/?action=view¤t=Growell0002.jpg