GUIDE深度 · Deep dive
Pool Chlorine Levels Explained
Free chlorine is commonly targeted at 1 to 3 ppm, but higher CYA requires a higher target. Total chlorine is free plus combined chlorine; high combined chlorine means shock.
Which numbers matter
Free chlorine (FC) does the sanitizing; combined chlorine (CC) is spent chlorine and above 0.5 ppm usually calls for shock.
CYA is often 30 to 50 ppm; higher CYA reduces the effectiveness of the same FC.
Estimating a dose
Raising 10,000 gallons by 1 ppm takes about 1.3 ounces of 65 percent calcium hypochlorite or 2.5 ounces of 12.5 percent liquid chlorine, as an estimate.
Test FC and CYA first, then follow the product label; do not guess.
FAQ
What if free chlorine is zero?
Test CYA and pH, add chlorine and retest; persistent zero may mean chlorine demand.
High total but low free chlorine?
That means lots of combined chlorine; shock is usually needed.