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!
Test for: Phosphates