Shocking and CC relationship -- question frrom newbie

[burine]

I have finally decided to take control of my pool and have been reading the Pool School and these forums the past few weeks, but I do still have a question regarding the shocking process and how it affects combined chlorine. I *think* I understand the relationship but want clarification/confirmation.

I understand that the TC = FC + CC. What exactly is combined chlorine? I originally thought that chlorine "combined" with the organics (e.g. algae) to produce CC but I don't think chemical compounds combine with organic material (I'm a few years out of school ) so that means the chlorine combines with other chemical compounds in the water to produce CC, but which what chemical? Shocking then oxidizes the CC into...what? How does adding more chlorine break down CC? And what is the result of that process, meaning does that produce other chemical compounds that have to be worried about?

If these questions can't be answered without a chemistry explanation, just tell me "that's how it is, deal with it" and I'll understand

 

[jblizzle]

Welcome to TFP!!!

I am sure this is discussed in a thread somewhere ... although it is likely rampant with chemistry explanations.

I don't understand the process myself, but the FC breaks down the organics and CC results, then the FC and sun break down the CC ... and then the pool is sparkly

Maybe someone else will stop by with more info ... possibly more than you want to know.

 

[JasonLion]

First, one chlorine combines with any of various compounds containing nitrogen, typically organics like algae but also things like ammonia, to form CC, breaking down the original organic compound in the process. Then a second chlorine combines with the CC and breaks things down to more fundamental compounds, like water, salt, and nitrogen gas, that we don't worry about.

If your FC level is reasonably high any CC created will be broken down fairly quickly and not enough will accumulate to create a measurable CC level. But if the FC level is quite low CC can be formed much more quickly than CC breaks down, leading to a measurable CC level.

Much more detail about the chemistry is available in this post.

 

[burine]

First, one chlorine combines with any of various compounds containing nitrogen, typically organics like algae but also things like ammonia, to form CC, breaking down the original organic compound in the process. Then a second chlorine combines with the CC and breaks things down to more fundamental compounds, like water, salt, and nitrogen gas, that we don't worry about.

Gotcha. Basically it combines with "stuff" and becomes used up. This also means that CC isn't really an indicator that algae is present, right? Since it can combine with non-algae stuff like ammonia?

If your FC level is reasonably high any CC created will be broken down fairly quickly and not enough will accumulate to create a measurable CC level. But if the FC level is quite low CC can be formed much more quickly than CC breaks down, leading to a measurable CC level.

I take it this is why people have said to shock the pool when CC gets too high. But what is "too high"? 1ppm? Is there an issue with having a high CC other than the smell and burning eyes I read about? Or is it that the OTO test kits become useless since CC skews the results (since they test TC)?

Much more detail about the chemistry is available in this post.

"that's how it is, deal with it"

 

[burine]

I don't understand the process myself, but the FC breaks down the organics and CC results, then the FC and sun break down the CC ... and then the pool is sparkly

I'm sure this is all I really need to know, but sometimes my brain wants to know they "why" of it hehe

 

[jblizzle]

Correct, CC does not necessarily mean algae ... ammonia will certainly show up as CC.

CC > 0.5ppm indicate that something is going on in the water that should likely be taken care of through the shock process. It will contribute to the smell and irritation as well.

We do not typically use the OTO for much. The test kits we recommend include the FAS-DPD chlorine test which is much more accurate and will test up to 50+ppm and give FC and CC individually.

 

[woodyp]

A good hot sunshiney day will also burn off excess CC..........up to 1.5 anyhow that I know of.

 

[burine]

We do not typically use the OTO for much. The test kits we recommend include the FAS-DPD chlorine test which is much more accurate and will test up to 50+ppm and give FC and CC individually.

Ignore the signature, FedEx still has my TF-100, hehe.

But, assuming a "negligible" CC of .5ppm, wouldn't an OTO test kit essentially report the FC level (I know it test TC) and use less expensive reagents to do so?

 

[burine]

A good hot sunshiney day will also burn off excess CC..........up to 1.5 anyhow that I know of.

Oh, I thought UV burns the FC only. Good to know.

 

[JasonLion]

If CC is essentially zero, which it usually is, then the OTO test will report the FC level. However there are two problems, the first is minor, the second is major. First, you don't ever know for sure that CC is zero, so in rare cases the OTO test can fool you. Second, the OTO test is exceedingly difficult to read at FC levels above 2 or 2.5, or to put that another way, most people can't distinguish between the colors from an FC of 3 to FC of 10+, and that is the range we use the most.

The OTO test is most useful as a quick chlorine/no chlorine test. Many people use it daily as a quick check that things haven't gotten completely out of hand, and get out a fancier test only once a week or when something is going wrong.

 

[burine]

The OTO test is most useful as a quick chlorine/no chlorine test. Many people use it daily as a quick check that things haven't gotten completely out of hand, and get out a fancier test only once a week or when something is going wrong.

This was essentially my plan once the TF-100 came in. But I have had the same issue with trying to match up the water color with the color chart. The water color was a "neon" yellow that didn't quite match with the chart. I figured that once I was reasonably sure CC was close to 0 I'd use the OTO to make sure there was chlorine in the water. As you said, if its difficult to read at FC above 2.5, as long as its above 2.5 I figured it should be good. Of course, I'm planning to use the TF-100 at least weekly once I can get into the swing of things (I expect I'll use it more often at first).