Red Sea Merlin Fluidized Bed Sand Filter up to 200 gallons. Water is supplied to the Merlin by a 150 gal. per hour, 5 ft. head pump (not supplied with the unit) and placed in the aquarium or sump. The water flows into the fluidization chamber through the central inlet tube which includes a non-return valve to prevent back-siphoning of the media. The water flows up through the fluidization chamber, fluidizing the media and is returned to the aquarium or sump via the outlet in the lid. Flow regulation: Rotation of the Flow Regulator (on the tope of the unit) sets the opening between the inlet tube and the fluidization chamber which determines the flow rate of the water through the unit. The fluidization level, therefore, can be adjusted according to the pump used and individual install