You could add a bit more light (new tubes) or just wipe off the algae with your fingers. I read where this algae occurs usually in the first 3 months after tank setup and can disappear as the tank stabilizes or where the florescent tubes are old. Otocinclus will eat brown algae.
its common in tanks that new. Keep wiping, it should be gone in a few months. If it gets out of control and doesnt go away even in a few months and you get large amounts daily, then we can consider otos. Just see how it goes i guess.