the aquachek phosphate teststrips test for: phosphates use the most accurate method for phosphate testing: a one step, one minute, phosphate test. even very low levels of phosphate can feed algae and create problems in pool water. test for phosphate once a week as the concentration in the water can increase rapidly due to rain, debris or bather load. results in a minute! for a clean and healthy pool, test the water at each end a minimum of twice a week.