The Lifegard Aquatics Flow Control Valve for Fluidized Bed Filter allows the hobbyist to control how quickly water passes through their Lifegard Aquatics Fluidized Bed Filter. The slower the flow rate, the more time the filter has to biologically break down toxins in the aquarium water, however you always want to be sure that the pump you are using can handle back pressure before using a flow control valve. Check to your pump's manual for further information.