The Two Little Fishies PhosBan Reactor 150 Adjustable Height Filter Plate is for use with soft media. The Adjustable Plate has a gasket that holds the plate into place. This is useful with soft media that you do not want to tumble causing the media to break up or to separate media layers within the reactor. Soft media examples are carbon and resins. The Plate can also be used with the Two Little Fishies Little Reactor and comes with a sponge as well.