Why We Shock at Night
Shock works best after the sun goes down, and honestly, there is one simple reason why. Ultraviolet sunlight eats chlorine, so a dose poured in at noon starts burning off before it can even get to work. By dinnertime, that midday shock has lost most of its punch, because it spent the afternoon fighting the sun instead of the algae.
At night, that same chlorine gets hour after hour of quiet, undisturbed work on the
algae and bacteria hiding in your water. The pump keeps running, carrying the shock evenly into every corner instead of letting it sit in one spot. By morning, the heavy lifting is done, and the chlorine level settles back down toward a safe range for swimming.
The Evening Routine
Wait until the very last swimmer climbs out, then brush the walls and the floor, slowly, so the shock can reach what is hiding. Then give the pool its evening dose, and let the pump run overnight while the water quietly does all the carrying. In the morning, before anyone jumps in, check the level, just to be sure it has settled back down.
And if your pool is truly green, one night may not finish the job, and that is normal. A second night of the very same routine is perfectly normal. It is not a failed treatment.
Key Takeaways
Ultraviolet sunlight eats chlorine, so a midday shock burns off fighting the sun instead of the algae and loses most of its punch by dinnertime.
At night, chlorine gets hours of quiet, undisturbed work on algae and bacteria while the pump carries it evenly into every corner.
By morning, the heavy lifting is done and the chlorine level settles back toward a safe range for swimming.
The routine: wait for the last swimmer, brush the walls and floor, dose in the evening, run the pump overnight, and check the level in the morning.
A truly green pool may need a second night of the same routine; that is normal, not a failed treatment.
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