Pen Plax QCF2 Replacement Cartridge for Clear Free II Filter (2 Pack) Cartridges is a no mess, quick easy replacement for the Clear-Free filter (CF2), as well as Water World 2 Aquarium Kit (WWA7) Replacement cartridge is made with foam/floss, carbon and zeolites Weight: 0.1900 lbs Cubes: 0.0007