Aquatopia Aquarium Coloured Gravel is epoxy-coated, which makes the gravel inert and prevents any adverse effects on water chemistry. Research shows that epoxy-coated gravel provides an optimum surface for the colonization of beneficial bacteria, which in turn provide biological filtration for clear and healthy water. These are an ultra-modern decorative highlight and a great addition to any small fish tank. The gravel is dust free and is available in a wide variety of colours. For fresh water and saltwater aquariums. Comes in 2 kg bag and black in colour.