【Quality Guarantee】-- Guarantee refund, if you have any dissatisfaction on the quality of goods, please contact us, we are willing to send you a new goods or a full refund. 【Wide Application】-- Our bio balls can be used not only in biochemical filtration systems in seawater, but also in biochemical filtration systems in freshwater, perfect for using as fish tank filter, aquarium filter media, pond filter media.PLEASE NOTE:16mm/26mm bio balls is perfect for Fish Tank and Aquarium, If you buy it for outdoor Pond, you'd better choose 36mm/46mm/56mm/76mm bio balls. 【Keep The Water Clear and Clean】-- Great help to restore the natural water quality, and provide the most suitable living environment for your fishes.Optional Type: 16mm/26mm/ 36mm/46mm/ 56mm/ 76mm. 【How to Work】-- When the water flows through internal space, prolonged the time, using the nitrifying bacteria to achieve the effect of biochemical filtration. 【Large Volume】-- Strengthened the effect of filtering bacteria, lightweight and easy to carry.