CaribSea pre-washed Super Naturals are designed with your success and ease of use in mind. Sizes and colors have been carefully selected to help you create a natural underwater environment like those of the Amazon River blackwaters or Asian jungles. These inert products will not affect your ph or alkalinity, allowing you to adjust these important water quality parameters any way you wish. Can be used in marine aquariums when alkalinity and pH are properly maintained. The sand is ideal for safe for soft-bellied fish and burrowers, and is suitable for marine and brackish aquariums with proper buffering. The 5 pound bag of Super Naturals Rio Grande has a typical grain size between 3.0 mm and 5.0 mm and features an average density of 93 pounds per cubic foot.