Replacement Two Little Fishies PhosBan Reactor 150, Washer NEW STYLE. Note: The Washer and O-Ring look similar. The Washer is flat and the O-Ring is rounded.
If the Washer you're replacing is rubber and 1/8" thick, this is the correct Washer. If the Washer you're replacing is very thin plastic (either black or clear), you will need the Two Little Fishies PhosBan Reactor 150, Washer NEW STYLE.
