Save money buying this BULK-size package that consists of four Marineland Eclipse Rite-Size Z Filter Cartridge 3-Packs (12 filters total). The Rite-Size Z is for the Eclipse System Three, Corner 5, Hex 5 and Hex 7 & all Explorer Aquarium filtration systems. It's also the replacement for the Marineland Silhouette, Contour 3 & 5 and Portrait Aquariums. For best best results, change the filter cartridge every 2-4 weeks.