Pool Shock (Calcium Hypochlorite).

Calcium hypochlorite granules — sold as "pool shock" — are the dry-powder form of chlorine disinfectant. Unlike liquid bleach, which degrades to ineffective levels within 6 to 12 months, dry granules sealed in their original container hold potency for a decade or more. One pound treats approximately 10,000 gallons of water. For long-term storage of chlorine treatment capability, pool shock is the most efficient option per dollar and per square inch of shelf space.

The baseline stock for most households is 1 pound. Buy only plain granular calcium hypochlorite at 68% or higher concentration. Check the label. Pool shock sold for residential pools often includes added algaecides, clarifiers, or stabilizers — none of these are safe for drinking water treatment. The active ingredient on the label should be calcium hypochlorite at 68%+, with no additional pool chemicals.

The stock solution method — required

You cannot add pool shock granules directly to drinking water. The concentration is far too high and the result is not safe. You must make a stock solution first, then dilute that solution into the water you want to treat. This two-step process is the EPA's documented method for calcium hypochlorite.

Storage

Store in the original sealed container in a cool, dry, ventilated location — away from heat, direct sunlight, moisture, and other chemicals. Moisture is the primary enemy: even slight humidity causes caking and accelerates potency loss. Do not store near acids, ammonia, or other pool chemicals. Mixing calcium hypochlorite with incompatible chemicals can produce toxic chlorine gas. Once you dissolve granules into a stock solution, that solution degrades quickly — mix only what you will use within a day or two.