Features: 1. Rational combination: Bio-Balls do not require replacement unless damaged or destroyed, Use scientific method, reasonable filter material, the filter media works better. 2. Effective: Resolve impurities,Stabilize PH,Clarify your water naturally. 3. Work as a biological filter media: Aquarium bio filter is excellent interaction between air and water and air exchange. They will promote air exchange and increase dissolved oxygen levels. So as to form a good ecological cycle. 4. Hollow Out: There is a hollow in the middle of the biological column filtering medium, can provide an anaerobic environment, reducing the content of nitrates in water, and promote more healthy water quality. 5. Great for any freshwater or saltwater fish tank or aquarium. Easy to wash and clean. Notice: 1. Actual color may be slightly different from the image due to different monitor and light effect. Please allow 1-3cm deviation due to manual measurement. Specification: Type: Aquarium Filter Media Main Material: glass, ceramic, stone etc. Style: includes 12 styles Include: 1 pack x 12-in-1 Aquarium Filter Media with storage bag Package List: 1 pack x 12-in-1 Aquarium Filter Media with storage bag