Someone told me this the other day (not from a forum but from an email) and it doesn't sound accurate to me: [media beds] are great for nitrification, but bad as clarifiers.  Generically they become clogged and need frequent mixing, and/or backwashing.  Fixed or movable media beds used as clarifiers also increase the Oxygen demand of the system, as many of the solids wind up being digested in the…