Thank you for your question. Brown sludge is an accumulation of organic waste materials. To keep sludge buildup to a minimum, begin by physically removing the brown sludge. A pond vacuum such as the WaterKeeper International WKII Large WaterKeeper #CE-70754 is an excellent tool for sludge removal. To maintain a low sludge environment, condition your pond with a bacterial additive. Microbe-Lift Sludge Away #CE-24855 is a natural bacterial additive that breaks down sludge and pond muck, perfect for this task.