Weco Nitrate-Reducing Filter Pad helps reduce nitrate in aquariums, which can cause fish stress. Great salt and freshwater use. Creates cleaner aquatic environment. Rapidly removes floating particulate organic debris for easier cleaning! Excellent quality and effectiveness! Designed and manufactured for aquatic professionals and hobbyists. Trim to fit any filter: canister, hang-on, wet-dry, internal or top filter, endless uses! Helps improve aquarium water quality. Chiseled design decreases bypass, prolongs usage and enhances fitment options. Package is designed with freshwater fish on one side and saltwater fish on the other to suit your stores display needs.