100g Black Volcanic Rock Biochemical Ball Filter Media Nitrifying Bacteria House Aquarium Filter Accessories For Fish Tank Water Cleaning Features: 1, From natural Volcanic Rock 2, Full of rich variety of natural elements and essential minerals and trace elements. 3, PH Neutral. Great help to restore the natural water quality, and provide the most suitable living environment for your fishes. 4, Won't dirt water, absorb ammonia, and other toxic substances in water. 5, Porous and will be good for Microbial reproduction. 6, Long life time. The little holes are not easy to be blocked. Type 1 :Black Volcanic Rock Specification Material: Natural Volcanic Rock Color: Black Diameter: about 3-8cm Including: 100g Black Bio Balls Filter Media Volcanic Rock Aquarium Filter Type2:Red Volcanic Rock Specification Material: Natural Volcanic Rock Color: Red Diameter: about 3-8cm Including: 100g Red Bio Balls Filter Media Volcanic Rock Aquarium Filter. Type3:Grey Natural Rock Biochemical Ball Filter MediaSpecification Material: Natural Rock Color: Grey Diameter: about 1-2cm Including: 100g Grey Bio Balls Filter Media Rock Aquarium Filter _x000D_