Dymax Aquarium Gravel is more than just an easy way to achieve a unique look in your tank – it helps to: anchor the ornaments and plants; hides waste and debris; keeps bottom sucking fish happy and even provides some biological filtration. Some species of fish prefer dark or light colour and may attempt to ‘blend in’ with certain shades of gravel. For aquascaping and landscaping purposes: pH neutral. Natural rocks and gravel from mountains; streams and rivers. Provides comforting habitat and shelter for fishes from stress. Large smooth stones measuring 40-50mm.