Tetra® Whisper® Bio-Bag® Disposable Filter Cartridges keep aquarium water crystal clear and remove s and discoloration. The dense dual-sided mesh catches debris and fish waste. Ultra-Activated® carbon absorbs s. 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 extra-large. Choose the medium size filter cartridge to fit the Tetra Whisper PF10 Power Filter 10i Internal Filter and Retrofitter® 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. The extra-large filter fits the Tetra Whisper PF 4 and 5 Power Filters