Two Little Fishies ATLPBR550 GFO PhosBan Reactor 550 Two Little Fishiest Hoban Reactor The Hoban Reactor Is Designed With The Up flow Principle To Achieve The Most Efficient Use Of Hoban Or Other Chemical Filter Media By pushing water from the bottom upward through a dispersion plate, it forces an even distribution of water through the media Two Little Fishies Phosban Reactor The PhosBan Reactor is designed with the upflow principle to achieve the most efficient use of PhosBan or other chemical filter media By pushing water from the bottom upward through a dispersion plate, it forces an even distribution of water through the media