Problem with CC

lburr

Member
Jun 15, 2018
8
Springfield, TN
I am having CC readings of 1 and 1.5 even though the water is perfectly clear. Sometimes it is .05, but when it reads higher, I increase the chlorine application. I have slammed a few times since opening and gotten good readings on the OCLT, including yesterday. Only lost .5 in FC overnight and the CC reading yesterday morning was 0. Since yesterday morning, the FC has gone from 13 to 6 and the CC from 0 to 1.5.

It keeps raining and there are some tiny gnat-like insects on the surface of the pool, but I don’t know what is causing this CC issue. No leaves. Pump runs 24/7. Polaris has the pool bottom so clean it has worn off the vinyl pattern.

this morning, pH is 7.5, FC is 6, Cc is 1.5
yesterday morning, early, pH 7.8, FC 13, CC 0
night before, after dark, FC was 13.5, CC .5
last CYA test was 30, about 48 hours ago.


any advice? How critical is the CC level? Is it safe for swimmers to use the pool when CC is 1 or 1.5? I would start SLAMMING again today but there are more thunderstorms forecasted and I don’t want to backwash all that bleach out into the yard if we have to lower the water level. If I keep FC in standard range during this week of rain, will the CC issue worsen?

thank you for any input.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,626
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40

CC- Combined Chlorine

Combined chlorine is an intermediate breakdown product created in the process of sanitizing the pool. CC causes the “chlorine” smell many people associate with chlorine pools. If CC is above 0.5ppm, you should SLAM your pool. CC indicates that there is something in the water that the FC is in the process of breaking down. In an outdoor pool, CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight.

Potassium monopersulfate (a common non-chlorine shock) will show up on FAS-DPD chlorine tests as CC. There is a special reagent you can get to neutralize the potassium monopersulfate so you can get a true CC reading.

The above is from ABCs of Pool Water Chemistry. It is safe to swim in the pool, but high CC can cause irritated eyes, dry skin, etc.

When you can, I would suggest raising your FC to SLAM level. That and some sunshine on the pool surface should clear up the CC reading.
Also be sure you clean the test vial with bleach. Sometimes that resolves a CC testing issue.
 

lburr

Member
Jun 15, 2018
8
Springfield, TN

CC- Combined Chlorine

Combined chlorine is an intermediate breakdown product created in the process of sanitizing the pool. CC causes the “chlorine” smell many people associate with chlorine pools. If CC is above 0.5ppm, you should SLAM your pool. CC indicates that there is something in the water that the FC is in the process of breaking down. In an outdoor pool, CC will normally stay at or near zero as long as you maintain an appropriate FC level and the pool gets some direct sunlight.

Potassium monopersulfate (a common non-chlorine shock) will show up on FAS-DPD chlorine tests as CC. There is a special reagent you can get to neutralize the potassium monopersulfate so you can get a true CC reading.

The above is from ABCs of Pool Water Chemistry. It is safe to swim in the pool, but high CC can cause irritated eyes, dry skin, etc.

When you can, I would suggest raising your FC to SLAM level. That and some sunshine on the pool surface should clear up the CC reading.
Also be sure you clean the test vial with bleach. Sometimes that resolves a CC testing issue.
Thanks for the tip about the test vial. Wiped it out with a bit of bleach and got aCC of .05. But the FC jumped from 6 to 8, even though I rinsed the test vial thoroughly. For good measure we have pulled up the two pool ladders and will wipe them down before reinstalling. Looks like there may be a bit of gunk on one of the rubber bumpers that rest against the side of the pool wall. Suspect that might be the culprit! Hope so.

thanks again.
 
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