Gravels are one of the most important part of aquarium because they keep water fresh and healthy long and long time by absorbing all the was they work as a good biological filter because most of the healthy bacteria grow between them they work as a great part in decoration these provide a very healthy environment to plant and fishes shining glow red color stones (gravel form) are available in 1kg pack, minimum 2.5 inch layer of gravels is very important for healthy aquarium.