What are you feeding it? I doesn't look too bad but don't look too good either. Make sure you are getting all the nutes in there and ph your water. It should prob be branching more. Yellow leaves usually mean N defficancy but it doesn't really look exactly what you have. Go to the GrowFAQ. Make sure you are giving it Cal and Mg that is a major problem that hurt me and took me a while to figure out. Kinda looked like what you have. Its all about experience. Research for yourself then try it out. It may take a couple weeks for it to get back to looking good.

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