Fluval active carbon filter foam pads are uniquely designed for Fluval FX canister filters. These carbon impregnated foam pads capture micro particles as the water passes through. The added carbon removes odors, discoloration, as well as heavy metals and organic contaminants.Fluval Active Carbon Foam Pads FX Series+ protects motor by trapping debris+ active carbon removes odors, discoloration etc and keeps the aquarium water crystal clear+ for fresh and marine water enviroments+ rinse frequently and replace every 4 weeks+ for Fluval External Filters FX4/5/6+ Package content: 2 pieces+ Fluval No. A249