Chlorine 4-Way Test Strips for Spa & Hot Tub Easy-to-read strips test spa water pH, total alkalinity,calcium hardness and chlorine levels. Features: Applications: Normal:Dip strip in water one time.Compare test results to chart on back of bottle. Tips: Low calcium hardness levels can cause foam and corrosivewater conditions, so use a strip that includesthe calcium hardness test. Compatible With: Chlorine, bromine and ozone sanitizers.