Indian aquarium fragments and gravel | Gravel | Stones and rocks | Decorative elements | Sand. The best types of substrates for aquariums | 25 kg. Type: Fragments Suitable for saltwater and freshwater Suitable for plants White gravel for decorating aquariums, where the white substrate can add a wonderful color contrast with rocks or other decorations in your tank. The white will truly shine against driftwood and rocky stones. Gravel is one of the most important elements in an aquarium because it keeps the water clean and healthy for a long time by absorbing all waste. It acts as a good biological filter where most healthy bacteria grow between them. It also forms a great part of the decoration. It provides a very healthy environment for plants and fish. A gravel layer with a minimum thickness of 2.5 inches is necessary for a healthy aquarium.