Most new tanks go through a stage of brown algae. If you get any kind of algae eater I recommend otocinclus catfish. They are little and cute, and after the algae is gone you can feed them algae wafers, and veggies such as cucumbers. However, you should only get them after your tank is cycled as they are sensitive to water conditions.
Be sure not to overfeed, and are the tubes in your light fixture fairly new? Old fluorescent tubes can put out poor light and contribute to brown algae outbreaks.