A high porosity filtration product for the removal and control of nitrate in marine and freshwater aquaria by anaerobic denitrification. It is a porous inorganic solid about 4 mm in diameter. It can be used in a canister filter at slow flow rates or even on the tank bottom as a “live” substrate. It does not require a special denitrifying filter or special culture feedings. It is also helpful in controlling nitrite and ammonia. The surface area characteristics of de*nitrate™ are similar to Matrix™ making de*nitrate™ an effective support for the biological filter. Each liter treats up to 100 gallons. Marine or fresh water use.