You can purchase sodium hypochlorite solution up to 15% concentration. I had a swimming pool years ago. The granular chlorine does not dissolve easily. It would be easier on you to buy it alreary in liquid form. In answer to your question, though, assuming a drum of solution weighs approximately 500 lbs, for 12% at 100% sodium hypochlorite would take 60 lbs, and 76.5 lbs of 73%