Tetra Whisper Bio-Bag Disposable Filter Cartridges keep aquarium water crystal clear and remove odors and discoloration. The dense, dual-sided mesh catches debris and fish waste. Ultra-Activated carbon absorbs odors. Use these replacement filter cartridges in your Tetra water filter – each package is color-coded to make it simple to remember which size to purchase. These replacement filters are assembled and ready to use for your convenience.