FAS-DPD powder question

[PoolDoc]

Honestly, with the DPD-FAS test, once you have color, you don't need more DPD.

[chem geek]

The amount of DPD powder will slightly affect how clearly you see the transition at the endpoint of the test where more powder results in a sharper endpoint (the chlorine oxidation of DPD dye to a colored form is an equilibrium mostly towards the colored dye but not completely). Are you using a 10 ml sample size or a 25 ml sample size? With a 25 ml sample size, one full scoop is usually needed to see a decent transition, but your half scoop might be OK for a 10 ml sample size. You can certainly experiment and see if it makes any difference for you since you're the one doing the measurements. Odds are it will only change your result by one drop at the most so not a huge deal.

[CarlD]

And, just as a reminder, with 10ml, one drop represents 0.5 ppm of FC and CC when testing.
So, as Chem_geek says, you won't be off by more than 0.5.