This unassembled replacement carbon filter helps keep aquarium water crystal clear and removes odors and discoloration. The dense, dual-sided mesh works to filter debris and fish waste. The color-coded cartridge is designed to fit Tetra Whisper water filters (sold separately). These convenient cartridges are easy to assemble and replace. Each cartridge provides up to 1 month of quality results. Help keep your aquarium crystal clear with Tetra's Bio-Bag Filter Cartridges. These disposable filter cartridges are easy to use and work to keep your fish tank in tip-top condition. The ultra-activated carbon is designed to absorb discoloration, contaminants and foul odors while the dense, double-sided mesh works to trap debris and fish waste. These Bio-Bags are designed to fit Tetra's Whisper 20i and PF10 Power Filters. Best of all, the three-stage filter cartridges are easy to assemble! Instructions Changing the Bio-Bag®: When water flows excessively from the Wonder Tube Chamber into the aquarium, it is time to change the Bio-Bag®. The Bio-Bag® should be changed once per month to prevent backflow and avoid filtration problems resulting from a clogged Bio-Bag®. Remove Bio-Bag® from filter, allowing excess water to drain into filter box. Remove clip from frame, fold up frame flap, and remove floss bag from frame. Place new floss bag over frame. Add one packet of Ultra-activated® carbon. Fold flaps of Aerobic Frame® over filter bag and replace clip. Rinse Bio-Bag®, insert into filter, replace filter cover.