De nitrate is an economical, natural, porous material with a pore distribution and geometry that promotes both aerobic nitrification within the first few millimetres of depth and anaerobic denitrification at the core. The material has a high surface area and supports a high density of bacteria. Although 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. “Live” rocks or reef rocks remove nitrate by anaerobic denitrification. 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 anaerobic environment to support denitrifying bacteria. De nitrate is also an excellent media for aerobic nitrification and it makes an ideal biological filter in drip trays, canister filters, sumps or even box filters. At high flow rates (greater than 100 us gallons per hour), it will function solely as an aerobic filter. At slow flow rates (less than 50 us gallons per hour), it will function as both an aerobic filter and an anaerobic denitrifying filter.