Cyanuric acid is an acid that is marketed as a chlorine “stabilizer” for swimming pools. It is also referred to as a “conditioner.” When exposed to the ultraviolet rays of the sun, the free chlorine in the pool water will break down and escape. Cyanuric acid is intended to reduce this loss of chlorine. Cyanuric acid is often a component of chlorine tablets used in automatic chlorinators. It is also available in powder form. Cyanuric acid residual remains in the water and will increase in concentration as additional amounts of cyanuric acid are added to the water. At high concentrations (>50 ppm), cyanuric acid can substantially decrease the effectiveness of chlorine.