<a href=showthread.php?s=&postid=10982242#post10982242 target=_blank>Originally posted</a> by xcreonx
the light isnt going to add phosphates to your tank. lights only help photosynthetic things grow, like hair algae. The algae will still need the right amount of nutrients in the water, which tap water and fish food certainly provide.
What is your water change schedule?
Since you used tap water previously, it's possible there's alot of left over heavy metals and junk from the water in your tank. Can you do a series of big water changes?