Whisper 40i Internal Filter and 3-Pack of Bio Bag Filter Cartridge Refills Whisper 40i Internal Filter and a Bonus 3-Pack of Bio Bag Filter Cartridge Refills Designed for Use in Medium-Size Aquariums Up to 40-Gallon, Uses Large Whisper Bio-Bag Cartridges Provides convenient 3 stage filtration Keeps water crystal clear Removes odors and discoloration