Not sure when to end FAS-DPD test

[evan567]

I'm performing the FAS-DPD test with a smart stir and I'm not sure exactly when I should stop adding drops. There comes a point where there is a sharp drop in color, and it looks clear while stirring, but when I pull it off the stirrer and look at it closely I can still see a slight red-tinge with red flakes. Adding a drop or two extra makes it even clearer.

Everything I'm reading says it should be completely clear but it also says the test should be performed fast and taking it off to closely examine the color adds time. So not sure if I should be going off the first sharp change or the more closely examined change.

 

[Bperry]

I'm performing the FAS-DPD test with a smart stir and I'm not sure exactly when I should stop adding drops. There comes a point where there is a sharp drop in color, and it looks clear while stirring, but when I pull it off the stirrer and look at it closely I can still see a slight red-tinge with red flakes. Adding a drop or two extra makes it even clearer.

Everything I'm reading says it should be completely clear but it also says the test should be performed fast and taking it off to closely examine the color adds time. So not sure if I should be going off the first sharp change or the more closely examined change.

The test is done when the water is clear. There may be tiny flakes still at the bottom but the water itself is clear.

If you leave the sample alone for a few minutes, it’ll start to turn pink again. That’s what the warning about doing it fast means. You can just leave it on the stirrer, no need to take it off.

 

[mgtfp]

Important is that it's colourless.

In rare cases the sample may turn cloudy. If this happens the test is still valid. You add drops until the sample turns cloudy white, i.e. the red/pink is completely gone, rather than waiting for it to turn clear.

From:

FAS-DPD Chlorine Test

The FAS-DPD chlorine test is used to find the level of Free Chlorine in the … Read more…

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