Aquarium filter media bags are meant to be used with the various chemical filtration media we carry: Carbons, Resins, Phosphate Removers, Biopellets & Organic Carbon, Metal Removers, & Nitrate Removers. Some of the chemical filtration medias come complete with flow through bags, and some don't. You can save money bagging your own media. All of our aquarium filter media bags are reusable. Useful Articles: Why Do You Need Aquarium Chemical Filtration?.