A white aquarium substrate can add a great contrast in colors from other rock or decoration in your tank, white will really stand out against bogwood and slate rocks. Gravels are one of the most important parts of the aquarium because they keep water fresh and healthy long and long time by absorbing all the waste. They work as a good biological filter because most of the healthy bacteria grow between them. They work as a great part of the decoration. These provide a very healthy environment for plant and fishes. The minimum 2. 5-inch layer of gravels is very important for the healthy aquarium.