Shop / Products / Estes Spectrastone Blue Gravel Estes Estes Spectrastone Blue Gravel Weight: 5 lb $14.99 Sorry, this product is currently out of stock. Information Ingredients Spectrastone blue gravel is an ideal substrate for fresh water and marine tanks. Our standard colors use silica quartz which is an inert stone that will not affect pH. N/A Customers also liked Customer Reviews