The Sulphur Nitratereductor SN Blue is an anaerobic biological reactor for removing nitrates in saltwater aquaria. An internal pump circulates the water through chambers containing sulphur beads and hydrocarbonate. Specialized bacteria develop inside the SN Blue that utilize sulphur as an energy source to remove nitrate. As a bi-product, sulphuric acid is produced, which is neutralized by the Hydrocarbonate in the filter. It comes complete with sulphur pearls and Hydrocarbonate. Rated for up to 270 gal. aquaria.