The FORZA 15-25 replacement cartridge insert is made of strong poly-fiber and collects organic debris for easy removal. Filled with AquaTop\’s Premium Activated Carbon, these replacement cartridges are extremely easy to install and help keep aquarium water crystal clear and free from odor. NOTE: AquaTop recommends replacing the Filter Insert filled with Activated Carbon every 4-6 weeks. Aquariums with heavier livestock loads may require more frequent replacement. Features: Replacement filter cartridge for the FORZA 15-25 Provides mechanical & chemical filtration Packed with Aquatop\’s premium activated carbon For best results, replace monthly 2pcs/pack *Also fits our Pisces Model Aquariums. PSC-RCI