CC questions - is some CC eliminated without shocking?

[lalittle]

Is shocking the only way to get rid of of combined chlorine, or can the normal addition of chlorine for general chemical balance eliminate small amounts of CC? In my pool, my CC is almost always 0 (i.e. not detectable using a Taylor FAS-DPD kit.) Every once in a while, however, I get a very low reading of around 0.2 ppm. After my normal dose of chlorine, my tests go back to showing 0 CC. Does this indicate that the small amount of CC was actually eliminated, or does it point to a small variation or error in the testing process?

I do know that during the FC test, the water can sometimes appear clear when it's still just barely pink. I'm careful to make sure that the water goes ALL the way to clear during the FC test, with NO residual pink, without adding any extra reagent.

On that note, does the addition of an extra drop of reagent during the FC test throw off the CC test? There are many times when the water seems REALLY close to clear, but not quite, so I add another drop. Usually I can see it clear up that last little bit, confirming the need for the last drop, but once in a while I feel like that last drop may not have been needed. It seems like this extra drop of reagent would cause the following CC test to be off by one drop because the first drop of the other reagent is "already there." Does the test work this way, or do the chemicals react in such a way that an extra drop during the FC test will not effect the subsequent CC test?

Thanks,

Larry

 

[JohnT]

Sunlight eliminates CC as well. Don't worry about anything less than 0.5ppm.

 

[loop_pea]

Yes, some CC will be eliminated by maintaining normal FC levels, although this can be masked if you have something lurking in the water that makes CC faster than you can bring it down. The process just goes a whole lot faster at shock level.

 

[rjg202]

I had the same concern, one day it is there, then it is gone. No issues here, and I have not really needed to shock except before we got dumped on by the hurricane.

 

[frogabog]

My take on CC is that it simply means your chlorine is actively working on something. If it's a small every day kind of something (dirty kids, organics, etc.) it's normal and less than .5ppm. It does it's job, the air and sunlight carries it away and then it's gone. Just like it's supposed to.

?? Am I wrong?

 

[lalittle]

Thanks for the responses.

Any feedback on the second question, i.e. (quoting from the first post):

I do know that during the FC test, the water can sometimes appear clear when it's still just barely pink. I'm careful to make sure that the water goes ALL the way to clear during the FC test, with NO residual pink, without adding any extra reagent.

On that note, does the addition of an extra drop of reagent during the FC test throw off the CC test? There are many times when the water seems REALLY close to clear, but not quite, so I add another drop. Usually I can see it clear up that last little bit, confirming the need for the last drop, but once in a while I feel like that last drop may not have been needed. It seems like this extra drop of reagent would cause the following CC test to be off by one drop because the first drop of the other reagent is "already there." Does the test work this way, or do the chemicals react in such a way that an extra drop during the FC test will not effect the subsequent CC test?

I realize that this would only make a 0.2 ppm difference in the result (when using the 25ml sample size), but I'd still like to fully understand all the parameters here. Knowing whether or not the extra drop influences the CC test will potentially allow me to be slightly more accurate with the CC test.

Thanks,

Larry

 

[Melt In The Sun]

I suspect you're right about that, but I don't know for sure either. It certainly seems that any excess of the R-0871 would decrease the indicated CC.

 

[chem geek]

Yes, whatever amount you overshoot the FC test will result in the CC test reporting that much lower. If you stop and count at the point when the color disappears, then you'll get a result to within one drop (or 10%, when the number of drops is large -- reason being that then the sample volume errors dominate).