Substrate is not just the stuff on the bottom of the tank, it plays a very important part of any aquarium system and each type of substrate is chosen for a specific reason and purpose, other than for cosmetic reasons and simulating the animal's natural habitat. Choosing the wrong substrate for your tank can create troubles, rather than solving the problem. If you choose to use a non-living media over live sand, it will become "live" as the tank goes through the cycling process and the aquarium matures. The best choice for substrate for Marine & Reef Aquariums is one that is naturally high in calcium content and that originates from the ocean. Aragonite, coral reef, and shell-based substrates are the most common choices, which can be purchased in various colors and come in a wide range of sizes from very fine to small grain, and medium to course grain. A recommended amount of substrate is with a thickness of approximately 1 ¾ to 2 inches, which calculates to approximately 1.45 pounds of substrate per gallon.