Marineland Penguin Bio-Wheel Power Filter Cartridges are designed to meet the absolute highest standards of water purification, performance and operational ease. Each replacement cartridge is pre-assembled and 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 poly fiber. Debris and waste particles are trapped, and water is chemically filtered through Black Diamond Premium Activated Carbon. Inside the cartridge, a patented ribbed backing ensures even distribution of activated carbon to deliver maximum water-to-carbon contact. The result is crystal clear, clean water. Features convenient, color-coded Rite-Size packaging to make it simple to choose the right replacement cartridge. For best results, change every 2 to 4 weeks. Clean, sparkling water is the mark of a healthy, thriving aquarium.