The volcanic rocks are a perfect addition to the bottom of your fish tank or aquarium, helping you create a beautiful underwater world! Features: Natural material: The volcanic lava rocks are 100% natural and safe which won't affect water's pH or chemistry and are suitable for both fresh and saltwater environments Decoration: With beautiful natural shaping, the lava rocks provide a colourful and detailed focal feature to your fish tank or aquarium Biological filter: These volcanic stones make for great natural biological filters that improve water quality, boost oxygen levels, and control nitrates for a cleaner and healthier habitat Wide applications: The volcanic rocks are also suitable for garden landscapes, planter beds, and other landscaping rock applications Specifications: Dimensions: H:8.0 x W:8.0 x D:8.0 cm Colour: Black Material: Stone Model Number: 3217185