Brown stuff? sounds like diatoms. If your tank is new, then don't bother doing anything, it is a phase and it'll pass as long as you keep your water parameters in check. Then you'll have green hair algea followed by cyano. This is normal for new tank.
On the cleanup crew: Trochus snails reported to eat diatoms along with other types of algae including cyano. For healthy sand bed, I'd recommend Nassarius and Cerith snails. They bury themselves in sand which will help maintain adequate oxygen levels in the substrate and eat detrius and uneaten food.
good luck