Brown algae is most likely diatoms. They are caused by excess silicates in the tank but too much lighting can be part of the problem depending on how much and how long your lighting is on. Is it a fairly new tank? These are common and they can be wiped off, you can use a phosphate remover if your tanks not planted, or in my opinion horned nerites are about the best diatom eaters you can get, plus due to their size they can get in most places. Bristlenose plecos and oto's also are very good at eating diatoms.