The Hagen A419 is the correct replacement phosphate absorbing cartridge for the following systems:
The Fluval G3 Replacement Phosphate Cartridge - A419 is a replacement filter for the Fluval G3 Filter System. This Fluval cartridge can quickly remove phosphate ions in your freshwater or marine aquarium. The Fluval G3 replacement also helps you maintain and control levels of phosphates, nitrates, and other organic pollutants to keep your water fresh and clear.
Fluval G3 Replacement Phosphate Cartridge - A419 specifications: