Grab a bucket of calcium hypochlorite (granular shock) or lithium hypochlorite (gentle but pricey). This is the old-school method, like using a sledgehammer to open a coconut. You’ll want to raise your free chlorine level to 10 times the combined chlorine level. So if your combined chlorine is 0.5 ppm, you need to hit 5 ppm free chlorine.
Wait for dusk—always at night! Sunlight eats chlorine like candy, so shocking at night gives it time to work its magic. Broadcast the granules around the deep end, run the pump, and let it marinate. In 12 to 24 hours, test again. If it’s gone, you’ve won. If not, repeat and try not to cry.
Pro tip: Don’t swim immediately unless you want to turn into a human chlorine test strip. You’ll glow in the dark (kidding, but seriously, wait until free chlorine is under 5 ppm).
