Dymax Filter Media Bags are available in various sizes and two styles, making them the perfect choice for storing popular filter media mediums like bio balls and ceramic rings. These sturdy bags are made of machine-washable nylon and feature a non-corrosive zipper. The breathable nylon material allows for free water flow and promotes the growth of beneficial bacteria, making them suitable for both freshwater and saltwater aquariums. Choose from Coarse Small or Coarse Medium sizes, each with specific dimensions for your convenience.