Seachem De-Nitrate

The media itself is a natural, porous, and economical material, featuring a pore distribution, shape, and large surface area that promotes beneficial anaerobic nitrification in the first few millimeters of depth and anaerobic denitrification at the core of the material.
Furthermore, the media helps remove nitrates, nitrites, ammonia, and harmful organic matter that can damage or even kill your aquatic inhabitants.
Live rock or reef rock removes nitrates through anaerobic denitrification, and Seachem De*Nitrate uses the exact same process, except that its efficiency is multiplied many times over thanks to the directed flow of water through the porous filter media.