This powder reagent is the first reagent for the FAS/DPD test for free chlorine and combined chloramines. 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. This 10 gram jar contains enough for about 100 tests. The jar is oversized to prevent spilling, so it will not appear full upon receipt. Exposure to humidity and light will darken this powder and cause it clump, but the powder is still usable and potent regardless. Simply crush the clumps back into powder and proceed with testing.