A filter system for filtering a liquid containing particles including a single media retainer plate having a top and bottom surface, and defining at least one hopper-shaped compartment having a sloped wall defining a slot spanning the top and bottom surfaces is disclosed. The plate also includes at least one baffle extending from the bottom surface and filter media disposed on the top surface. During a filtering operation of the filter system, the filter media captures the particles, such as dirt, from the liquid as the liquid passes through the filter media to an underdrain system. During a backwash operation of the filter system, the baffle is adapted to direct a backwash fluid in a vertical direction through the slot so that the backwash fluid actuates the filter media to scour the top surface of the plate and prevent the build-up of biological scaling on the plate.