yellowing leaves

well im currently growing one full moon platn and one white rhino. i am on my third week and the new nodes come out a perfect green. however my lowest nodes yellowed so much they died. my next set of leaves are a light light green. and then i have my top third node which is a perfect green color. so pretty much as the nodes start to show they increasingly turn more yellow.

Check out this site: http://www.marijuana-seeds.net/Thanks-ThankYou.htm It talks about common plant problems, yellowing of leaves, overwatering, etc...

Here's another site that might be useful, I'm unsure what to say without pictures of the plant. http://cannabis.com/growing/index.html

Are your nutirents balanced? How's your nitrogen? Are you using re-used soil? Hydro? Are you running your lights all day? Ph level?

just snip them off