Tetra Whisper Unassembled Bio-Bag Filter Cartridges Easy to Assemble, Easy to Replace Whisper Bio-Bag Cartridges complete the Whisper Power Filter-Package for a clean, easy-to-maintain aquarium Easy to Assemble, Easy to Replace The Whisper Bio-Bag multi-packs come unassembled and offer economical pricing on larger quantities. Three stage filtration