Rite Size Filter Cartridge B fits the Penguin 125/150 Bio-Wheel Filter. Each preassembled cartridge slides easily into place, providing superior mechanical and chemical filtration, and making replacement fast, dry and effortless. The cartridge mechanically filters water through a pad of double thick polyfiber. Debris and waste particles are trapped, and water is chemically filtered through Marineland's Black Diamond Premium Activated Carbon.