- Description AquaChek Yellow | AquaChek Tests for: Free Chlorine, pH, Total Alkalinity, Cyanuric Acid (Stabilizer). Ideal for customers who use chlorine as the sanitizer in their pool or spa. Includes a test for Cyanuric Acid (Stabilizer), which is especially important for outdoor pools and spas which are subject to chlorine dissipation from UV rays. Get 4 important test results in just one dip! Just dip an AquaChek Yellow strip in your pool or spa water for one second and remove it immediately. You get test results in seconds! To keep you pool water clean and healthy, test the water at two ends or sides of the pool a minimum of twice a week!? If used in a spa we recommend testing it before and after each use. It’s also a good idea to write down your results each time you test.