Replacement Bio-Wheel Assembly for the Marineland Penguin Power Filter. The Bio-Wheel is the most important stage of filtration in your filter system. It creates the most ideal surface area for the colonization of beneficial bacterias that will biologically filter your aquarium water, freeing it of harmful levels of both ammonia and nitrite -well known fish killers. You should only replace your bio-wheel if it is broken and falling apart. Inconsistent rotation and a generally foul looking appearance is normal for a well established Bio-Wheel.