Dpd test question

kimkats

Mod Squad
LifeTime Supporter
Jul 10, 2012
36,600
Tallahassee, FL
#2
The FAS/DPD powder test: Measuring chlorine VERY precisely, even up to 50ppm+

The liquid test is really a more of "yeap there is chlorine in the water" kind of test.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,633
Tucson, AZ
#3
Yes and no @kimkats

The yellow OTO chlorine test is useless except as a “presence of chlorine” test.

The liquid DPD test (R-0001/R-0002 Taylor reagents) is accurate as an FC test but has limitations because it’s a color comparison test. So the color swatches have to have enough saturation difference in order for the human eye to register a color difference. This results in slightly wider ranges as you go up the scale.

The DPD-FAS test (the “powder” test) is the exact same chemistry as the liquid DPD test only one uses the FAS titrating reagent to force a color change (pink to clear) which is a lot easier for the eye to see. This results in better accuracy.

I use the liquid tester (DPD color comparator) all the time for daily spot testing of FC and it is dead-on accurate with the powder test. I use the DPD-FAS test only when I want to know the FC/CC accurately.


Pro tip - If you use the FAS titrating reagent (R-0861) with the liquid DPD test and you know how to do the math, you can get exactly the same results as the powder test ;)
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,633
Tucson, AZ
#5
A K-1004 test kit (DPD color comparison for FC, pH, acid demand, TA) is a decent test kit to own for doing quick daily checking and I would even recommend it for hot tub owners. If all one wanted was the liquid DPD test, then the K-1001 kit has that. The DPD color comparison is better in my opinion especially if one gets the #9056 high-range comparator block from Taylor (FC 1, 2 , 3, 5, 7.5, 10ppm and a pH comparator). The ranges are a little wide but the color contrast are easy enough to see so you know roughly where your pool is at. I use this all the time for my pool and reserve my R-0870 powder for more accurate Saturday morning testing.