What lights are you using? They should be closer those stems are pretty long.
I think your plant might be suffering from nute loss maybe Nitrogen?
Not to be an asshole dude, but if you don't know what you're talking about don't give your two cents. A plant that small does not need more nutes while growing in MG soil. That plant has nute burn, and if the OP had listened to you and put in more N his little girls would be fucked. MG soil is hard on seedlings, and a difficult soil overall to grow in. However, I've seen a lot of pics of some nice looking bud that was grown entirely in MG soil. You just have to know precisely what you are doing. Do not add anymore nutes to that soil.
What lights are you using? As jcurry26 already mentioned, you will want them closer. Use your hand as a guide. Put your hand a few inches under the light. If it doesn't get overly hot on your hand, you can lower the lights. Once they are low enough to where they begin to burn your hand, raise them just enough so that it doesn't burn anymore. I'm guessing you're using CFLs since it's a PC grow though, and CFLs should be no further than 2 inches from your plants, unless they are the higher wattage ones. In which case, use the hand method.
Lastly, if that is foil in there, I recommend pulling it out. If you can afford it, buy some mylar and put it up. If you can't justify forking out the cash for an entire roll of mylar for such a small area, just pain the inside of the box with flat whtie paint. Either of those two things reflect light nearly twice as good as foil. Foil is designed to create heat, which it does very well. It isn't designed to reflect light.
Hope that info helps, and good luck. Keep us posted!
! Im using MG pottong Soil and tap water with a seed i got in a bag of smoke! I dont have alot of cash so what is a cheap way to fix this? what is the problem!! I have included a video so you can see my problem!!Thank you
