It is totally a natural substrate of aragonite oolitic period (spherical or egg-shaped cone) for all types of reef or marine aquarium. Meridian is a premium quality aragonite substrate for reef aquariums. The grain size (an average size of 0.25 to 0.5 mm uniform) is ideally suited to bring the inhabitants of the reef and its chemical composition will help to stabilize the calcium and alkalinity preventing large pH declines. Unlike products "wet" marketed by our competition under the concept of containing living, Meridian is sold dried, sold and you pay only for the gravel and water unnecessary. These products indicate that contain live animals and microscopic priate in fact contain only common bacteria. Dry or wet, there are bacteria in each substrate available. If one is concerned with shortening the cycle time of the tank in a Brand New, use a product designed for that particular purpose to be more appropriate (such as Seachem Stability).