Whisper 3i Internal Filter and 2-Pack of Bio Bag Filter Cartridge Refills Whisper 3i Internal Filter Plus a Bonus 2-Pack of Bio Bag Filter Cartridge Refills Designed for Use in Smaller Aquariums Up to 3-Gallon, Uses Small Whisper Bio-Bag Cartridges Provides convenient 3 stage filtration Filter Cartridges are Filled With Ultra-Activated carbon, removing waste particles, odors, and discoloration Keeps water crystal clear Removes odors and discoloration