First time growing, 2/40w fluorescent + 60 w cfl, HELP Needed

Hey! I was just wondering if someone could tell me what's wrong with the leaf. Some older leaves are also like that... Second picture, stem is turning purple. any reason?

THANKS
(growing power plant)

Are you giving it nutrients? how old is your plant?

yes, they get 20-20-20 every week/half and they are 3 months
thanks for the reply

LOOKS LIKE AN INSECT/PARASITE TO ME. COOD BE a red spider.
http://www.youtube.com/watch?v=a3Q1xqZoLsg sorry link is in spanish. pretty much resumes the simptoms of the " red spider"

your plants look way way way to small for 3 months? stems turn purple when its to cold

That leaf is one of the smallest. And its always around 70 to 80 in the room. Too cold?