Save your aqua friends from any dirt particles with the Marina i25 replacement power cartridge. It is made specifically to fit inside the Marina i25 internal filter. As water flows from the two-chambered cartridge, it first passes through the zeolite chamber, removing all the toxic ammonia. The water then enters the activated carbon chamber, where pollutants and odours are removed. It further enters the floss layer, which traps dirt and debris, resulting in crystal clear water. For best results, replace it every four weeks. This package contains two power cartridges.