Two Little Fishies PhosBan Reactor 150 O-Ring Two Little Fishies Phosban Reactor Rubber O-Ring The PhosBan Reactor is designed with the upflow principle to achieve the most efficient use of PhosBan or other chemical filter media It can be mounted hanging on the back of the aquarium or below the aquarium. Two Little Fishies Phosban Reactor O Ring The PhosBan Reactor is designed with the upflow principle to achieve the most efficient use of PhosBan or other chemical filter media It can be mounted hanging on the back of the aquarium or below the aquarium It can be mounted hanging on the back of the aquarium or below the aquarium