Ideal for fish tanks, to promote gas exchange and increase dissolved oxygen levels. Ideal for tropical fish farms, ponds, wastewater systems, etc. For use with wet/dry filters (here is not included), to improve filtration. Help in the critical gas exchange process that is necessary for successful filtration. Color: Black Material: Environmental Plastic Dia: 16mm Package List: 300 * Bio Balls Only the above package content, other products are not included. Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3 cm.