How sensitive is the FAS-DPD test to the amount of DPD powder used? This morning when I tested my water I used 2 scoops of DPD powder. The first scoop turned the water pink as it usually does and then I added the second scoop. In this particular instance both scoops were just a little less than level, but not by much. When I added the drops it only took 5 drops to turn the water clear for an FC reading of 2.5. Yesterday evening I tested and came up with 4.0. Now, my water is sparkling clear and all the other test levels are right where they should be so I was a little suspicious. I decided to redo the test, using the same sample of water but this time using just a tiny bit more than a level scoop and sure enough it read 4.0. Is the test that sensitive to the amount of powder used?