Reasons for incorrect CC reading

Sep 1, 2021
Pool Size
Liquid Chlorine
I recently tested my water, and the CC reading was pretty high. It was at 3ppm when I've never seen anything over .5ppm (even then not sure it was real, sample had the faintest pink after adding the R-0003). I retested to confirm, and neither the FC or CC chlorine readings agreed with the first test.

I then did two things before another re-test:
1) Cleaned the test tube (with soap/water). There seems to be some buildup from testing on the tube.
2) Used the second container of the R-870. The first is almost gone, seems a little clumpy, and the end of the dipper is stained black by now.

The FC and CC chlorine readings showed what I expected after this (FC as expected based on time since last test, and CC between 0-0.5ppm). I then retested with the first container of R-870 and got the same results (FC as expected, CC=0-0.5).

My two theories are:
1) Test tube had some residual chemicals on it that corrupted the test. This seems most likely because after cleaning the test tube I got consistent results with both R-870 containers.
2) R-870 gets clumpy over time, and didn't fully dissolve before I added the R-871. Then when I added the R-003 the pink color wasn't from CC but from FC that didn't register when adding the R-871 because the R-870 hadn't dissolved yet.

My first guess makes more sense, but that makes be curious about any affects that the R-870 powder has as it ages. It seems to get clumpy, and the dipper get stained black as time goes by, do either of these impact test results?



Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I vote for 1.

If the R-0870 turns the water red then it is good. It is just an indicator chemical.
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