Also, the resolution of the test is only one drop (or 10%, whichever is greater) so going clear after one drop means <= 0.5 ppm. It does not mean you have 0.5 ppm CC. If you really wanted to know with more precision what you have, then use a 25 ml water sample instead of a 10 ml water sample. You add a heaping spoon or two level spoons of DPD powder, still use 5 drops of the R-0003, but each FAS R-0871 drop represents 0.2 ppm FC or CC instead of 0.5 ppm. I'll bet that your sample turns colorless after just one drop meaning you have <= 0.2 ppm CC.
In an outdoor residential pool exposed to sunlight, CC is rarely a concern. It's really used more as an indicator that something may be wrong and as a hint that there may be ammonia or organics in the water that are not getting oxidized fast enough though even then only certain types of chemicals will show up with intermediates that last long enough to measure as CC. You can have zero CC and still have an unusual chlorine demand. So of all of our measurements, CC is probably the least critical and the absence of CC doesn't mean everything is AOK. Even when CC is present, it is rare to have someone notice it (i.e. smell it) unless it's very high or they have a serious water problem such as an algae swamp.
