Whisper 20i Internal Filter and 3-Pack of Bio Bag Filter Cartridge Refills Whisper 20i Internal Filter and Bonus 3-Pack of Bio Bag Filter Cartridge Refills Designed for Use in Smaller Aquariums Up to 20-GallonUses Large Whisper Bio-Bag Cartridges Uses large Whisper Bio-Bag Cartridges (Bonus 3 Pack Included) Provides convenient 3 stage filtration Conveniently Assembled and Ready-to-Use