WIO Black Venom Gravel S is a gorgeous aquarium substrate. Glossy black when wet or matt grey coloured when dry, these rounded stones are excellent for mixing with other similar types to create a wonderful layout in either an aquarium or terrarium. They are great when combined with WIO Black Venom Stones and Boulders, so much that Aquascapers love these for adding detail to their masterpieces. WIO Black Venom Gravel ever so slightly raises the pH level of aquarium water. Particle sizes 8-20mm. Available in 2kg packs.