The AquaClear Quick Filter Replacement Cartridge gives you two spare internal media inserts for your powerhead filter. The extra-thick duo-density pad is made from finely woven polyester to trap particles and debris and has an expanded capacity to remove solid wastes. It works in both marine and freshwater tanks to help keep the water clear and free of waste. So， help keep your aquarium in tip-top shape for your fish friends with AquaClear!