Our aquarium substrate is 100% natural slate gravel with a unique deep grey blue color. It has been sorted into a beautiful blend of sizes to create a realistic and natural look in your aquarium. The color is a matte grey blue with a small amount of brown stone and white quartz bits that add to the natural look. Our gravel is aquarium safe and absolutely beautiful an a planted tank as the grey color makes the plants and other inhabitants pop. For Aquascaping, this gravel pairs very well with our Natural Slate Stones that come in a variety of sizes up to 10 inches (25cm) long to create a natural scene in your tank. This stone is inert and does not alter the pH.