Stabilized vs unstabilized chlorine on the skin.

[JesseWV]

Yesterday I was wondering what the difference is between getting out of a pool with only an appropriate level of FC and no CYA and a pool with both FC and CYA.

I'm trying to figure out if failing to rinse off in the shower after swimming in a pool with FC: 9 and CYA: 80 is better or worse than failing to rinse after swimming in a pool with FC: 2, CYA: 0

I can think of a few things going on here, drying, oxidizing and higher UV exposure due to 0 water depth.

What effect would this have on your skin as the water dries? I wonder if the equilibrium begins to quickly break down causing the CYA to rapidly release the bound chlorine? It also seems likely that there is more to oxidize on the surface of your skin than in a volume of water which would also cause the CYA to release it's stores.

Just something to ponder....

 

[duraleigh]

chem geek has the precise answer but I remember that the 2 FC and O CYA setup has MUCH more active chlorine and is tougher on swimwear.

 

[Durhamhouses]

I read in the Taylor Test kits manual that there is some health concerns around CYA in general and especially at over 100ppm and that some jurisdictions do not allow it's use at all ..just something else to ponder

 

[teapot]

From Chemgeeks info, the 2ppm and no CYA is way over the equivalent on the Chlorine/CYA chart. In a pool with no CYA you would have an equivalent if you had 0.1ppm free chlorine. I have no CYA in my pool and run with 0.2ppm free chlorine (I am using/testing a replacement for CYA)

 

[JasonLion]

The practical difference is very very small. Without CYA there is a slightly higher chance of having a chlorine smell after you get out, and otherwise you would be hard pressed to notice a difference. The chlorine will all break down and turn to salt in seconds, or minutes at most, even with CYA. And even the quantities of salt are too small to be noticeable.

 

[JesseWV]

The practical difference is very very small. Without CYA there is a slightly higher chance of having a chlorine smell after you get out, and otherwise you would be hard pressed to notice a difference. The chlorine will all break down and turn to salt in seconds, or minutes at most, even with CYA. And even the quantities of salt are too small to be noticeable.

I was wondering whether it is even necessary to rinse off after swimming in water with most of the chlorine bound by CYA. If it were to remain stable it shouldn't cause any irritation at all.

Looking at the PoolEquations spreadsheet I notice that at my CYA level of 80 and FC of 9 I have:

OCl- (as ppm Cl2): 0.052
HOCl (as ppm Cl2): 0.057

Thats only 0.109ppm total (am I doing that right?)

I was mainly concerned about all of the bound chlorine being released all at once. I realize it would be used up oxidizing your skin very quickly but thats precisely what I'm trying to avoid.

 

[JasonLion]

You will never notice it. The amount of chlorine involved is tiny compared to the amount of organic material involved.

 

[dmanb2b]

I read in the Taylor Test kits manual that there is some health concerns around CYA in general and especially at over 100ppm and that some jurisdictions do not allow it's use at all ..just something else to ponder

Do you happen to have a link? or reference to which manual?

 

[chem geek]

Though it is true that chlorine with CYA on the skin will react more slowly, that isn't usually the only factor. You usually continue to sweat so in practice it isn't the reaction rate that is so important but rather the total chlorine capacity, so that would be the FC level. Assuming there is enough sweat or other compounds on the skin for chlorine to oxidize, then it is the FC that matters, independent of CYA, because that's how much Combined Chlorine (CC) will be produced, such as monochloramine or other compounds that smell. So getting out of a pool with no CYA might have a brief peak of smell, but in a pool with CYA and a higher FC there might be a less intense smell that continues longer.

So while in the pool it is the FC/CYA ratio that is relevant to the rate of reactions on swimsuits and skin, once you get out it's more about capacity or FC for the final affects of chlorine. Also, as the water evaporates, the chlorine will become more concentrated. So in theory, the higher FC may bleach out the swimsuits more, but this is probably a fairly small effect compared to being in a pool with no CYA. From my wife's experience with her swimsuits, I would say that having no CYA in the pool water during an hour or so of swimming is more relevant than the hours outside the pool until she rinses the swimsuit (which she always does). If she never rinsed the swimsuits, then the higher FC might become more noticeable.

 

[Durhamhouses]

Do you happen to have a link? or reference to which manual?

Taylor Part # 2004B "Pool & Spa Water Chemistry"

 

[dmanb2b]

Do you happen to have a link? or reference to which manual?

Taylor Part # 2004B "Pool & Spa Water Chemistry"

Thanks, unfortunately could not find it for download. Do you mind sharing the specific concern Taylor cautions readers regarding CYA usage?

 

[JasonLion]

dmanb2b,

I read in the Taylor Test kits manual that there is some health concerns around CYA in general and especially at over 100ppm and that some jurisdictions do not allow it's use at all ..just something else to ponder

What they are most likely talking about is people who have CYA around 100 and still maintain FC around 1 to 3 just like always. That can be very problematic. There are indeed some laws about CYA levels in public pools, with some areas limiting CYA to 100, and others outlawing CYA completely. Again these are based on failing to understand the FC/CYA relationship.

 

[dmanb2b]

Thanks Jason. That's exactly why I questioned the reference. That makes sense.

 

[Durhamhouses]

Jason has it right for the most part but it does briefly mention toxicity as well. While saying no known cases have been heard of, CYA poisoning is a concern in some states ...but I couldn't find any other pool related references on the web when searching google on "Cyanuric Acid toxicity". I tried scanning it but its grey print on blue paper and I'm too lazy to transcribe it.

 

[chem geek]

This document gives a summary of toxicity data for Cyanuric Acid. Though it isn't something that one would want to ingest in concentrated form, it's not toxic when diluted and it has minimal skin absorption.

 

[Speedo]

Imagine all those people testing with strips on "pool store" pools using pucks and cal hypo, etc.... mine last year. Who knows what my CYA really was.

I used trichlor 1" tabs and cal hypo for about 2 weeks or so after opening AND I probably have 2000 gallons or so of newly added tap water. My CYA is still above 90 after almost 2 weeks of no trichlor or cal hypo. But I also have the solar cover on most of the time.

 

[efm1972]

dmanb2b,

I read in the Taylor Test kits manual that there is some health concerns around CYA in general and especially at over 100ppm and that some jurisdictions do not allow it's use at all ..just something else to ponder

What they are most likely talking about is people who have CYA around 100 and still maintain FC around 1 to 3 just like always. That can be very problematic. There are indeed some laws about CYA levels in public pools, with some areas limiting CYA to 100, and others outlawing CYA completely. Again these are based on failing to understand the FC/CYA relationship.

Jason - what are the problems that can arise with FC ~ 1 to 3 and CYA ~ 100?

 

[JohnT]

dmanb2b,

I read in the Taylor Test kits manual that there is some health concerns around CYA in general and especially at over 100ppm and that some jurisdictions do not allow it's use at all ..just something else to ponder

What they are most likely talking about is people who have CYA around 100 and still maintain FC around 1 to 3 just like always. That can be very problematic. There are indeed some laws about CYA levels in public pools, with some areas limiting CYA to 100, and others outlawing CYA completely. Again these are based on failing to understand the FC/CYA relationship.

Jason - what are the problems that can arise with FC ~ 1 to 3 and CYA ~ 100?

With CYA that high, 1-3ppm FC is essentially unsanitized. The CYA slows the activity of the chlorine quite a bit.

 

[chem geek]

A 1 ppm FC with 100 ppm CYA is equivalent to less than 0.01 ppm FC with no CYA. It will take 10 times longer to kill bacteria and oxidize bather waste compared to an FC that is around 10% of the CYA level. So a 3-log (99.9%) reduction in fecal bacteria would take around 8 minutes instead of 48 seconds or so. At 1 ppm FC with 100 ppm CYA, half the fecal bacteria are killed every 50 seconds while with an FC that is 10% of the CYA level it's every 8 seconds.

So in practice, the water is still sanitary in terms of preventing uncontrolled bacterial growth, at least for fecal bacteria. It may not, however, be fast enough to prevent person-to-person transmission of disease so would be of greater concern in commercial/public pools.

Now for Legionella pneumophila, a 1 ppm FC with 100 ppm CYA would kill half in about 1 hour so would not quite kill it faster than it could reproduce while an FC that is 10% of the CYA level would kill half in about 6 minutes, so faster than it can reproduce.

 

[MoreSparkle]

Chem geek thanks! That is so cool! - to understand why something works the way it does... I think I am going to take my test kit to the municipal pool with the FC/CYA chart if we ever make it there this summer.. Son likes jumping into the deep end.. Can't do that in ours.. So we may go.. Of course we won't stay long if the readings aren't good!!! Yes I want the water sanitized around me!!!! ESP with other kids in it! Thanks, love reading your answers