Quick FC/CC question

[barnyard]

I am confused. I opened the pool today. The water was clear but there was a lot of debris on the bottom. I use a winter mesh cover, so I guess that explains that. Anyway, with all the debris I figured I would raise my chlorine to shock level which is 16, after I checked the CYA. Anyway, I got it to 16 at 1:30 pm and it had 0 CC. I checked again at 3:30 pm and it was down to 11, and again no CC's. I thought that you would have CC's if something was eating your chlorine, or am I mistaken? Anyway, I raised it again, probably overshot it so I will check again before bed time. I was just curious about the CC's or lack of CC's.

BTW, to everyone that says they loose all their CYA over the winter, you had better check. This was the first year I haven't lost my CYA. I was all set to shock with powdered stuff since I figured I would need to add CYA anyway. Boy, am I glad I checked first. My CYA was exactly where it was the last time I checked it last year before closing. That is a first.

 

[Richard320]

Hmmmmm

You'll lose some FC to sunlight, period.

I'm wondering sortof aloud here.....
1) did you actually measure 16, or was it calculated? Becasue if the bleach was last year's leftovers - yours or the store's - it may not be as strong as indicated. 2) How well mixed was the water? You may have gotten a strong sample area, and now it's mixed better.
3) If you had no FC, you would have no CC initially. But now you have FC and it's working on organic debris, so it's disappearing.
4) You don't know what's in the pipes or filter, could be stuff lurking in there.
5) If you used the 10ml sample for the FAS-DPD test, you can be off on CC. I would test and get numbers like 4.5 FC, .5 CC. Using the larger sample, I ended up with 4.8 and .2 respectively. If I got impatient, I could have easily added one more drop and gotten 5 and 0!

Again, just wondering aloud.

 

[woodyp]

Here is something I copied from one of the resident gurus on the forum that might help............................................Combined Chlorine (CC) is mostly chlorine combined with urea (probably monochlorourea and dichlorourea) since urea is the largest component of sweat and urine. The second largest component is ammonia so chlorine combined with ammonia, mostly monochloramine, is also registered as CC. So long as you still measure reasonable Free Chlorine (FC), the pool is safe, but much higher CC levels can be smelly and irritating. If your pool doesn't smell bad, then the levels of CC in the pool are probably not irritating. It's an indicator and nothing to panic about.

The long and short of it is that having CC's doesn't necessarily indicate any organic growth (algae).
Somebody correct me if I'm wrong on this.

 

[barnyard]

well, I did mesure 16. But I did test after only about 1/2 hour or so, so maybe the water wasn't mixed well. No sunlight since it is cloudy and raining here today. The pool is clearing up nicely, so I am not going to spend too much time worrying about it, I was just curious. All is well that ends well.