Marineland Rite-Size Cartridge E -12 Total Cartridges (3 Packs with 4 per Pack) 12 Total Cartridges (3 Packs with 4 per Pack) Marineland Rite-Size Cartridges (Size E) Color-coded packaging ensures fool-proof cartridge selection Delivers crystal clear, crystal clean water Meets the highest standards of water purification and operational ease