Tetra Whisper Bio-Bag Disposable Filter CartridgesWhisper Bio-Bag Cartridges complete the Whisper Power Filter package for a clean, easy-to-maintain aquarium. Filled with Ultra-Activated carbon, the ready-to-use disposable single packs remove waste particles, odors and discoloration, and are easily changed once a month. The Whisper Bio-Bag multi-packs come unassembled and offer economical pricing on larger quantities. It is recommended that you replace your Whisper Bio-Bag when water begins to overflow excessively from the Wonder Tube chamber, or once per month. Small fits Whisper Power Filter 3i.Medium fits Whisper Filter MicroFilter, 10i & External Power Filters E, J & 10.Large fits Whisper 20i, 40i & External Power Filters C, 20, 30, 40 & 60.