For the ultimate in convenience, choose this 3-Pack of Assembled Whisper- Bio-Bag- Cartridges. Offering the same protection as the traditional Bio-Bag-, the 3-Pack is packaged in a color-coded carton, making it easier than ever to remember which cartridges to purchase. Replace your Whisper- Bio-Bag- Filter Cartridge once a month, or when water begins to overflow excessively from Wonder Tube- chamber.