Which pool shock is better: sodium dichlor or calcium hypochlorite?

Sodium dichlor is easier and more convenient—just toss it in—but it adds cyanuric acid, which can lock up chlorine if overused. Calcium hypochlorite is stronger and cheaper per pound, but it raises pH and calcium hardness, and must be pre-dissolved to avoid bleaching surfaces. Use dichlor if stabilizer is low, calcium hypo if it’s high.