I
Inundated in SF
Guest
It happens almost always in new tanks. It's just a brownish-green algae that takes advantage of the imbalance of the tank. You can get a small algae eating fish like an couple otocinclus catfish (only grows to be 1.5", very peaceful fish, eats mostly algae if it can get it but will also eat raw zucchini and parboiled green beans and spinach if there isn't enough algae) or algae eating snails. Every time you tear down your tank, you are starting from scratch, have to cycle the whole tank again, and will get brown algae on everything. Try not to have to tear down your tank.