Whisper 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. INFO FROM UNITED PET GROUP