A method and system for filtering water in aquarium tanks comprising: a macerating/comminuting chamber with a continuously self-cleaning screen covering the discharge outlet that only allows, optimally sized, easily digestible, organic material to pass out of the macerating/comminuting chamber and into an, optionally self-cleaning, media containing denitrifying microbes. There are three different embodiments that use the method of the current invention. These comprise: a reverse flow under-gravel filter apparatus with the macerating/comminuting chamber and filter screen on the discharge side of the pump, a reverse flow under-gravel filter apparatus with the macerating/comminuting chamber and filter screen on the inlet side of the pump, and an external box filter apparatus with the macerating/comminuting chamber on the discharge side of the pump.
