The Marina 360 / Marina Splash Replacement Filter Cartridge, with carbon and zeolite, improves water clarity and color while removing polutants and odors. This replacement filter cartridge is designed for use with the Marina 360 Aquarium and the Marina Splash Aquarium. The Marina 360 / Marina Splash Replacement Filter Cartridge comes in a package of 4.br /> Also available on this listing are 3 x packs of 4 this will keep you stocked up for 6 months as the requirement for changing them is between 2 - 4 weeks.