Here’s the nerdy part, but I promise it’s painless. The general rule of thumb is: 1 pint (16 ounces) of 3% hydrogen peroxide will lower your free chlorine by about 1 ppm in 10,000 gallons of water. Most drugstore peroxide is 3%, so that’s your sweet spot.
If you have 35% pool-grade hydrogen peroxide (the strong stuff), you use way less. For that, it’s about 1 ounce per 10,000 gallons to lower chlorine by 1 ppm. But seriously, stick with the 3%—it’s safer, cheaper, and you don’t need to wear a hazmat suit.
Let’s do a quick example. Say your pool has 20,000 gallons and your chlorine is at 10 ppm. You want to lower it to 3 ppm—that’s a drop of 7 ppm. For 3% peroxide, you’d need 7 pints (112 ounces). For pool-grade 35%, you’d need only 7 ounces. Math is your friend here.
