Why isn't my hammer bright green like in the lfs?

[Spyd]

I think a bit stronger lighting than a single T5 would help. What colour bulb are you using? Also, the browning is far more likely caused by your nitrates. No coral likes nitrates that high. Having some in a LPS tank is fine, but not anywhere near that high. Bi-weekly water changes and a skimmer should keep nitrates down.