This reagent is used in the test to determine your cyanuric acid (CYA) level, and this size bottle is specifically fit to the TF-Pro case. R-0013 CYA Reagent is mixed with an equal amount of pool water in the CYA mixing bottle. Then, the mixture is added to the CYA view tube until the black dot in the bottom of the tube is completely obscured. The required amount of the mixture determines the CYA level of your pool. The bottle contains 2 ounces, enough for around 8 tests using the TF-Pro view tube.