Seachem de*nitrate is an economical, natural, porous material with a pore distribution and geometry that promotes both aerobic nitrification within the first few millimeters of depth and anaerobic denitrification at the core. The material has a high surface area and supports a high density of bacteria. Although Seachem de*nitrate has capacity to trap nitrate, this, as with other nitrate retaining materials, such as certain zeolites and synthetic resins, is quite limited and the primary mechanism of nitrate removal is anaerobic.Liverocks or reef rocks remove nitrate by anaerobic denitrification. Seachem de*nitrate removes nitrate by the same process. Efficiency is magnified several folds by forcing the water to filter through the porous de*nitrate. As with reef rock, anaerobic conditions are achieved by the porosity and the depletion of oxygen by the aerobic process at the surface. Excessive flow rates should, therefore, be avoided, as they may impede development of an adequate anae