I need help determining the correct FC level.

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
91
Homer, AK
I have been using the Lamotte Color Q pro since the pool opened in early June. It always gives me a reading for FC in the ballpark want: 1.5 to 2.0 ppm. I also have a Taylor K-2005 kit that uses the pink water color comparison test which I do not use because of the inaccuracy. So a few weeks ago I bought the R-0871 (FAS-DPD Titrating reagent and the R-0870 the powder that turns the water sample pink. I always get a much higher result from the FAS-DPD test than with the Color Q pro. Today the Color Q gave me an FC result of 1.87 ppm. I immediately did the test with the Taylor as follows: fill the large tube up to 25 ml level, cap and mix thoroughly. Then add two scoops powder with the tiny spoon, mix thoroughly and it turns pink. Then added R-0871 titrating reagent to the tube dropwise while counting the drops until the water in the tube turns from pink to clear. I was careful to mix up the water in the tube thoroughly as I went along. Today, I added 19 drops. This is multiplied by 0.2 and the result is 3.8 ppm free chlorine. Does anyone have an opinion as to which one is correct? Am I doing the Taylor FAS-DPD test correctly? The procedure I followed is taken directly from the Taylor website.
 

CrystalRiver

Well-known member
Jun 19, 2020
435
Massachusetts
You say you filled the tube to 25 mL, capped and stirred. Stirred what?

I use 10 mL sample because 0.5 accuracy is plenty. 10 mL pool water, then add the Speed Stir bar. Turn on Speed Stir. Add one scoop powder. Count the drops and divide by two.

As for which is more accurate, the drop kit or the meter, the answer is the drop kit so long as you followed proper procedure. Make sure you hold the drop bottle vertically and squeeze slowly so gravity takes the drops.
 
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