Free chlorine

Free chlorine is the number that tells you if your pool is safe today. A test that shows zero means the water has no protection left. Algae can bloom within days in North Texas heat.

CDC guidance for public pools sets a minimum free chlorine level of 1 ppm (parts per million). Backyard pools in strong sun often need more care to hold that level, because sunlight burns chlorine off fast. Test often, and read the label on your chlorine product. If free chlorine keeps falling, check your cyanuric acid and look for rising combined chlorine.