These AquaChek Yellow test strips from Hach will test your pool and spa water for free chlorine, pH, total alkalinity and cyanuric acid. Just dip a strip into the water for one second, and remove immediately. You'll have your test results in 15 seconds. To keep your pool at its best, test at each end of the pool at least twice a week, and test your spa before each use. Bottle contains 50 test strips. Instructions included in 15 languages.