South Ocean Five AOF00412 Nylon Filter Bag for Aquarium Filter, 4 by 12-Inch Filter bag can be used for various media, such as phosphate removers, nitrate removers, carbon and ammonia remover Made from 100-percent polyester with a polyester tie cord Sewn with 5-string merrow machine with a full safety stitch inside It prevents filter mediums from spreading and is made of heavy nylon for better water flow Measures 4-inch width by 12-inch height