This reagent is used in the FAS/DPD chlorine test to determine free chlorine and combined chloramines. This bottle contains 2 ounces, enough for around 140 routine tests. Please note, if your chlorine levels are very high due to the "shock" or "SLAM" process then you will use significantly more of this reagent per test and will not have enough for 140 tests.
In the FAS/DPD test, R-0870 is added to pool water to produce a color change to pink. R-0871 is added to produce a color change back to colorless (clear). The number of drops required is divided by 2 to determine free chlorine level. Then, R-0003 is added to return the color of the solution to pink and R-0871 is again added to return to colorless. The second number of drops required is divided by 2 to determine combined chloramines level.