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 easy to assemble and easy to replace. Clear water made simple.Replace a clogged Bio-Bag filter cartridge when there is reduced water flow out of the filter. For best results, change your filter cartridge monthly or sooner if needed. Size medium.Choose the medium size filter cartridge to fit the Tetra Whisper PF10 Power Filter, 10i Internal Filter and Reptofilter 90 GPH; and choose the large cartridge to fit the Tetra Whisper 20, 30, 40 and 60 Power Filters and 20i and 40i Internal Filters.Since 1951, Tetra has developed the world's most comprehensive body of fish food knowledge, and fishkeeping enthusiasts have looked to the brand for products and solutions that add ease and beauty to their home. Whether you're an experienced hobbyist or just starting out, Tetra has everything you need – from a large variety of quality fish food and innovative equipment to test kits and decor.