Where we mention Rx Clear Mega Shock | 73% Calcium Hypochlorite | One Pound Bags | 12 Pack

• Pool Shock: How to Raise Free Chlorine Safely

  Highest-strength cal-hypo · Best for: Maximum-strength single dose; 73% available chlorine

• How to Lower Cyanuric Acid in a Hot Tub

  CYA-free chlorine, conditional on calcium hardness · Best for: Cal-hypo carries chlorine and no cyanuric acid, so the number you just drained to fix stops climbing. Use it only while calcium hardness stays under about 200 ppm; above that the added calcium is what drives scale in a 100-degree tub.