Features: Perfect Filtration: Aquarium filter bio ball that helps clean your water naturally, beneficial to oxidation of oxygen convection exchange, and for reproductive growth with a huge surface area. Max Surface Area: Bio-sponge inside provides more surface area for growth. Many flake structure, internal porous, great for any freshwater or saltwater. Better Effect: The bio ball is idea for external and pressurized filters in aquarium for tank, pond filter and fish farm. Bio balls can be used loose or in the mesh bag with plastic zipper. Well Packed: 50/100pcs bio balls are packed in filter media bag, which bag is zipper closure design, reusable, easy to clean old media out and refill. Occasions: Suitable for water garden for ponds, freshwater fish tanks, saltwater aquariums, aquaponics, fish hatcheries and much more. Specifications: Material: Plastic Each Square Size: Approx. 36x36x34mm/1.42x1.42x1.34 inches Each Round Diameter: Approx. 33mm/1.3 inches Type: Square with sponge core, Round without sponge core Package Includes: 2 Package Optional: Package A: Includes 50 Pieces Square Bio Balls Filter Media Package B: Includes 100 Pieces Round Bio Balls Filter Media note: 1.Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item.