Hagen Part #A-578LargeTwin PackStandard foam cartridge provides extra circulation without endangering fishThe AquaClear Quick Filter Replacement Cartridge 2pk has an extra thick duo-density pad that has expanded capacity for waste removal. This thick pad allows it to remove solid waste and particles as small as 1 micron without difficulty. Exclusively designed to fit the Hagen AquaClear Powerhead Quick Filter Attachment.