Elive AquaDuo Aquarium Fish Tank Water Filter Replacement Cartridges, 6 Pack Healthy Fish: AquaDuo Filter Cartridges help keep water clear and fish healthy. Perfect Conditions for your aquarium Long Lifetime: AquaDuo filter cartridges last up to 4 weeks depending on the amount and species of fish Easy Installation: The cartridges are easy to swap and are linkable for use in filters that require multiple cartridges Perfect Fit: Fits all Elive AquaDuo aquarium filters Trusted Name: Elive has been a high quality manufacturer of aquarium equipment for many years and is proud to be the most trusted brand for aquatics in the US today. For use with Aqua Duo 10 and 20 Filters Cartridge Size - Medium Available in 3 or 6 pack Linkable Filter Cartridge Filter Floss and Sponge for Mechanical Filtration Activated Carbon for Chemical Filtration