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 are available in 5kg pack, minimum 2-2. 5 inch layer of gravels is very important for healthy aquarium.