Arag-Alive achieves rapid cycling by preparing and seeding the substrate grain surfaces with a wide variety of marine bacteria, most in a spored state, including strains engineered for maximum waste reduction capacity. Some types of bacteria reduce nitrogenous waste by metabolic oxidation while others incorporate nitrogen into bacterial biomass during rapid growth. Since most species of bacteria are somewhat symbiotic, and tend to colonize a surface in succession, the process of cycling an aquarium is facilitated by the close proximity of the immobilized species. Bacteria are maintained at a low metabolic rate by restricting access to certain limiting factors required for metabolism. The Eco-Complete freshwater products work in the same way, just with freshwater bacteria. This soft pink colored, 100% aragonite substrate is a good intermediate sand size product. The precise 0.5 - 1.5mm grain size combines some of the animal friendly properties of fine sand such as ingestability and low resistance to burrowing, but with better diffusive flux properties and good porosity. This is also the standard choice for reef aquariums at 1 pound per gallon.