The Hagen A1421 is a replacement filter pack for the following:
The Fluval Chi Replacements - 3 Filter Pads & 1 Foam is a replacement filter pack for 5 gallon and 6.6 gallon Fluval Chi Aquariums. This Fluval Chi replacement includes three filter cartridges and one foam biological cartridge. These aquarium filter pads provide superior chemical and mechanical filtration to help maintain a healthy aquarium environment.
Fluval Chi Replacements - 3 Filter Pads & 1 Foam specifications: