Ocean Free Square Cata-Pure Cartridge for Hydra 20/30/40/50 (4pk) The Cata-Pure Cartridge can last 9-12 months depending on the amount of fish and is functional in marine environments. Fits all model Hydra Internal Filters, Hydra Filtron &...

Ocean Free Square Cata-Pure Cartridge for Hydra 20/30/40/50 (1pk) The Cata-Pure Cartridge can last 9-12 months depending on the amount of fish and is functional in marine environments. Fits all model Hydra Internal Filters, Hydra Filtron &...

Ocean Free Hydra 50 Impeller Shaft Replacement Impeller Shaft for Ocean Free Hydra 50 Internal Filter Impeller sold separately.