What are your phosphates and nitrates like?
To combat it you could hook up a small fuge with some macro algea or buy some snails. How long has your tank been set up if it is only new and is going through the cycle then the brown algea (diamtoms is my best guess) should clear up as the cylce finishes. If not, better to find the casue of the problem then to get rid of the algea.
lol hope that made sence.
HTH
Josh
