In The Swim Pool Chlorine Stabilizer & Conditioner - 8 lbs.
Chlorine stabilizer reduces chlorine loss caused by the sun's ultraviolet rays.  Adding stabilizer greatly increases chlorine effectiveness and can actually cut chlorine consumption by up to 25% a year. 100% Cyanuric Acid. Dosage: Use 2-1/2 pounds per 10,000 gallons of water.  Do not over-dose, it is important to gradually increase the stabilizer level as it is very difficult to reduce once it has gotten too high.  Stabilizer levels should be maintained at 30-50ppm.