Brown algae are diatoms presumably from silicates and should go away by itself overtime if undisturbed, although in my case it never went away, I've tried waiting it out (had for over a year), keeping nitrates low, cleaning it with every water change, etc... Nothing worked, until I got myself a bn pleco, the brown crap was gone completely in a matter of days and I've yet to see it.
I did consider Zebra Nerrites snails (probably not a bad way to go).