Dymax Filter Media Bag is a zip type filtering bag made with a non corrosive plastic zipper with washable nylon mesh material that provides durability and flexibility for filtration applications. This bag can be used to hold filter materials such as: activated carbon; zeolite: ammonia remover resins: ceramic rings: phosphate remover and many others. This provides a convenient method to customise aquarium purification. Durable and stretchable. Suitable for freshwater and marine aquarium.