FAS-DPD Test Question

[phalcon51]

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?

Gary

 

[JasonLion]

If you use too little powder you will get a lower than actual test results. But if you use too much powder, within reason, there is no effect. The amount of powder you need to use goes up as the FC level goes up, so normally with FC levels around 4 it isn't very sensitive to the amount of powder used, while at high FC levels it becomes more important to make sure you are using enough.

 

[phalcon51]

Thanks Jason.