Brown algae = diatoms
Is the tank new (< 6 months old)? If so, they will eventually go away on their own. They should be easy to wipe off in the mean time though.
Otos will get rid of diatoms quickly, in my experience. The problem then is feeding them afterwards. They are not picky but shouldn't be added to a tank solely for algae eating purposes IMO. They are not the hardiest fish either...best for an established tank.