Biological Filter Ceramic Rings - 500 grams in Nylon Mesh Media Bag with PLASTIC zipper (not metal) to prevent rust/oxidation! &bull; Aquaculture &bull; Ponds &bull; Aquariums by Cz Garden OUTSTANDING FILTRATION! Each bio ball is covered in spines to dramatically increase the surface area of each ball to nearly 2 square feet providing space for a massive number of beneficial bacteria to colonize. These good bacteria break down harmful organic waste keeping your aquatic friends safe. You will receive approximately 50 bioballs (1.5 inches) in a ready to use black mesh zippered bag. Just rinse and use. TOUGH AND UNIQUE! Our bio balls spherical shape and precise spine placement permits them to pack tightly into any shape or filter type without losing surface area. Molded from high density plastic, these balls are lightweight but tough enough to keep their shape and will never degrade or wear out. Bio balls can be used loose or in the mesh bag with plastic zipper in which they are packaged. TRUSTED POND MEDIA! Our Bio balls are 100% polypropylene making them a safe reliable bio filter media for fresh and saltwater. They are manufactured for use in koi and water garden ponds, freshwater fish tanks, saltwater aquariums, aquaponics, fish hatcheries and much more. SUPERIOR TO LAVA ROCK: Over time, porous lava rock becomes clogged with debris decreasing its surface area so that its ability to house and grow good beneficial bacteria plummets. Our pond bio balls uniquely spaced spines allow most debris to pass right through them. Lava rock has tiny pores which make it difficult to clean while bio balls in most applications never need cleaning. A bag of wet lava rock is many times heavier than our pond balls. Only available from Cz Garden Supply (TM), USPTO and Amazon Brand Registry Protected