Quartz sand is a natural product and free of lime. With a grain size of only 0-1 mm, it is very fine and available in three colors. The substrate can be designed with sand, gravel, or a mixture of both, taking into account the needs of the fish. The average gravel should be rounded and have a grain size of no more than 2-3 mm. A gravel layer of 6-8 cm is recommended to allow plants to develop sufficient roots. Amazon gravel provides a fair and natural substrate for all fish species and their habitats. You can calculate how much gravel you need for your aquarium using the following formula: (Length x Width x Gravel Height x 1.6) / 1000.