Onyx Sand, 7 kg / 15.4 lbs Fracted Porous Substrate For The Aquarium Specially Fracted Porous Substrate For The Aquarium; Suitable For Most Marine And Freshwater Environments Including Reef And Planted Aquariums Most effective when used alone as an integral substrate bed but may be mixed with other gravels or sands Not Chemically Coated Or Treated But Does Have A Slight Buffering Capacity