Emperor Size E Fits all Emperor BIO-Wheel filtration systems. Replace cartridges every 4-6 weeks as needed. Package of 2. The Rite-Size filter cartridges contain faster-acting Black Diamond premium activated carbon for maximum mechanical and chemical filtration efficiency. Heavy-duty plastic frame with floss and carbon traps dirt effectively. Each pre-assembled aquarium filter cartridge slides easily into place, providing superior mechanical and chemical filtration, and making replacement fast, dry and effortless.