Degradation of Cyanuric Acid (CYA)

chem geek

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dschlic1 said:
On my pool I am seeing about a 10 ppm loss per month of CYA. CYA went from 70 to 60 ppm with FC between 3 and 4 ppm. Water temp is 90 F. During the month I did not pump out any water, and the only water added was from rain. My chlorine demand is about 1 ppm per day.
We hear about this more rapid loss in very sunny areas like Florida and Arizona. Not only will the water be warm, but the sun is pretty intense and on the pool for long periods of time. I wonder if sunlight can act as a catalyst for CYA breakdown. It does breakdown chlorine (hypochlorous acid and especially hypochlorite ion) so perhaps the intermediate free radicals that are formed (•OH •O- •Cl and subsequently •OCl •OH) may oxidize the CYA a bit faster. This is pure speculation on my part, though is based on some reactions described in this PDF file.

The question about Calcium Hardness (CH) is very relevant since it could indicate whether dilution is a factor (that's why I tracked that carefully in my own pool).
 

mas985

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May 3, 2007
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I'm not sure if this also has an influence or was just a coincidence, but last year we had quite a few fires near us and the sky was filled with smoke and ash. I noticed a lot of ash in the filter and all over the yard. During this period, the CYA in the pool dropped by almost half. I didn't see the same decline this year so I can't think of anything that was different last year than this year which would have caused the disappearance of CYA.
 

chem geek

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Ash as a catalyst or causing interference in the test? Seems very strange to me. As waterbear said, we really just have to TEST the water's CYA level every now and then and adjust accordingly. It would certainly be nice to know what really is going on in these situations when it drops, but until we do then testing will at least let us maintain a Trouble Free Pool.

Richard
 

spishex

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Oct 12, 2008
1,375
Hillsborough, NC
mas985 said:
I'm not sure if this also has an influence or was just a coincidence, but last year we had quite a few fires near us and the sky was filled with smoke and ash. I noticed a lot of ash in the filter and all over the yard. During this period, the CYA in the pool dropped by almost half. I didn't see the same decline this year so I can't think of anything that was different last year than this year which would have caused the disappearance of CYA.
That's interesting. Bioguard used to sell something called Absorbing Agent" for it's biguanide line. It was just activated carbon. I don't know if there's any on shelves anymore, but I assume you could use ground up charcoal in it's place. A worthy experiment.
 

alohaptd

New member
Aug 7, 2009
1
Just found this note on the LaMotte site:

Cyanuric Acid: Cyanuric Acid (CYA) = CYA tests are temperature sensitive. The best results are obtained when sample temperatures are between 70 and 80 degrees. In cold water, results may read high, while in warm water they may read low.
link: http://www.lamotte.com/testingtips/Colo ... 20Tips.pdf

This runs contrary tot he idea that in colder water precipitation rate would be lower.
Any ideas?
 
G

Guest

alohaptd said:
Just found this note on the LaMotte site:

Cyanuric Acid: Cyanuric Acid (CYA) = CYA tests are temperature sensitive. The best results are obtained when sample temperatures are between 70 and 80 degrees. In cold water, results may read high, while in warm water they may read low.
link: http://www.lamotte.com/testingtips/Colo ... 20Tips.pdf

This runs contrary tot he idea that in colder water precipitation rate would be lower.
Any ideas?
Precipitation rate is slower but solubility decreases in cold water so if you let it develp to completion it will read high since more will precipitate out. Likewise, in warm water less will precipitate since solubility increases. The speed of the precipitation has nothing to do with the solubility of the precipitate. The reaction will procede faster in warm water than cold water. LaMotte specifies a temerpature range and time range for the test because that is how their meter is calibrated. This time and temp range does vary smewhat with the different meters they offer.
There is no discrepancy.
 

chem geek

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I just updated the first post in this thread to show bacterial chemical pathways that allow further oxidation of ammonia to nitrate and nitrogen gas. This should resolve the mystery of disappearing CYA that does not result in high chlorine demand. Unfortunately, it is not easy to control which pathways are used since some are aerobic (require oxygen), some are anaerobic (are without oxygen), some require organic carbon and most are accomplished by different bacteria. At a minimum, nitrifying bacteria (such as Nitrosomonas) are required to convert ammonia to nitrite followed either by nitrifying bacteria (such as Nitrobacter) to convert nitrite to nitrate or denitrifying bacteria to convert nitrite to nitrogen gas or Annamox bacteria to convert nitrite and ammonium ion to nitrogen gas.
 

chem geek

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I ran into this paper describing how many organic compounds (including urea) are broken down in photocatalytic conditions when there is titanium dioxide (TiO2) in the water, but that Cyanuric Acid is resistant to such degradation. It also appears that CYA is resistant to degradation from hydroxyl radicals which makes sense since they are likely formed in chlorinated pool water exposed to sunlight yet we do not find CYA degrading very much over time. However, this paper indicates that when fluoride ion is added to the titanium dioxide, then the CYA is degraded in photocatalytic conditions by homogenous phase hydroxyl radicals (heterogenous generation of hydroxyl radicals from titanium dioxide is somewhat inefficient at 4-5% so the success from fluoride ion is probably mostly due to the much higher efficiency so higher quantity of hydroxyl radicals.
 

Isaac-1

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May 10, 2010
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SW Louisiana
I did not feel like paying $40 to read the article, so I will ask, does this mean that we should expect to see a higher rate of breakdown of CYA in pools filled from Fluoridated municipal water supplies?
 

chem geek

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No, because there shouldn't be titanium dioxide in the water. On the other hand, some sunscreen has titanium dioxide though it is coated with aluminum hydroxide to prevent reacting with water and sunlight to produce hydroxyl radicals. However, in this paper summarized in this article they found that chlorine can break down the aluminum hydroxide coating and the bare titanium dioxide would then react in sunlight to produce hydroxyl radicals. So if the pool had fluoridated water, then yes that would improve the efficiency, but I doubt that any of these amounts are enough to result in substantial CYA reduction, but I can't be sure of that.

Note that the coating degradation was observed when the chlorine level was 0.4 ppm and this was over 7 days. Remember that the level in our pools, due to CYA, is effectively more like 0.1 ppm.

Don't forget that when chlorine breaks down it forms hydroxyl radicals, but the quantities are rather small -- enough to keep residential pools in decent shape in oxidizing some organics, but not so much as to be the problem they are talking about with sunscreen. The titanium dioxide concentrations in sunscreen are much higher than the chlorine concentration because they are intended to be used as the primary UV block.
 

FluffyRAM

Member
May 31, 2013
6
Statesboro, GA
I'm new to TFP and stumbled across this thread while searching for CYA information.
I thought to add my experience since it seems to support the findings discussed above.

We purchased a house, complete with pool in December 2012. It had been for sale for almost a year but the pool water was immaculate because it was under "pool store care". Being new homeowners we couldn't afford to pay someone else to take care of the pool so we chose to 'learn quickly'!

Being pool newbies, the first thing we did was pick up an AquaChem pool care guide in Walmart and follow their 4-step program (I know, I can hear you all slapping your foreheads in dismay!). We used up all the chemicals left behind with the home purchase and wasted a fortune on the AquaChem way.

As spring approached and the water warmed up, we were quite pleased with ourselves that we had a beautiful clear sparkling pool.
Then summer arrived; hot and humid coastal GA summer - and we started to use it in earnest a few weeks ago. Did I mention we were just using the 6-way test strips?!!

Everything seemed great until you guessed it.... almost overnight - green algae bloom.

Fortunately, that's when I discovered this forum and The Pool School!
I patiently converted to the BBB method, got rid of the algae, and learned about DE to clear up the cloudy aftermath.
I had our pool back to clear and chemically balanced happiness, the day before we went to summer camp with the boy scouts.

I forgot to ask our neighbors to throw some bleach in while we were away (won't make that mistake again!).
So of course, we came home to a green pool again!

Green pool. Blah! Not too worried - I know how to fix it now (and I invested in a TF-100)

Tested. No chlorine. No surprise.
Being a newbie I nearly didn't bother testing CYA again since I thought it didn't change much. Wrong! I was surprised to discover a huge drop in a week, from 70 to 20.

Here's the history:

Day before we left:
Chlorine: FC 6, CC 0.5
pH 7.8
TA 145
CH 155
CYA 70
Water temp 86F

Using The Pool Calculator, I added bleach at green algae shock level and muriatic acid to lower pH to 7.2, leaving the jets up to aerate, the goal being to lower TA.
I suspect I hadn't quite killed all the green algae from the previous bloom and it got a quick hold.
We had a couple of days full-on southern sunshine, then phenomenal amounts of rain (our rain gauge was full meaning over 5.5" during the week we were gone).
I had to empty some water from the pool when we got home because the water level was too high.

Today's results:
Chlorine ZERO.
pH 8.2
TA 120
CH (not tested)
CYA 20
Water temp 86F

The weather forecast is for a lot more rain and cloud so I thought the low CYA levels would actually help the Chlorine be more efficient to kill off the algae while the sun is not a problem but I thought I'd better find some CYA ready to raise the levels as soon as the sun arrives again. I was on here searching for CYA sources when I found this interesting thread....
I've used bleach to green algae shock levels again today.
We won't be swimming until the algae clears but we'll be adding more muriatic acid to get the pH back down (and depending on my CYA source, it may get some help).

Hope this adds to the data for the chem-geeks out there.

Happy pool time :)
 

chem geek

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Total precipitation in Statesboro, GA in June, 2013 was 6.95" so if your pool has average 4.5' (54") water depth then that's a dilution of 12.9% so not that much. So I think the bulk of the CYA loss was bacterial conversion, but if you are able to hold an FC level (i.e. it doesn't get used up in minutes forming CC), then you may be very lucky that such conversion went to nitrogen gas rather than getting stuck at ammonia or partially oxidized CYA. Let us know what it's like for you adding chlorine to get rid of the algae, specifically whether you are able to have the FC hold at all for an hour.

It's too bad we can't more readily control bacterial conversion of CYA to nitrogen gas, preferably in a way that still limits algae growth, as that would be a fantastic way to lower the CYA level.
 

chem geek

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For CYA degradation, it goes through the following steps so depending on where it stops you can end up with a mixture of different chemicals that will behave in different ways and you can get a mixture of any of the following:

CYA ---> Biuret ---> Allophanate ---> Ammonia ---> Nitrite ---> Nitrate
........................................................... | .............. | .............. |
........................................................... | ....... Nitric Oxide ... Nitrite
........................................................... | .............. | .............. |
........................................................... | ..... Nitrous Oxide ...... |
........................................................... | .............. | .............. |
........................................................... | ..... Nitrogen Gas ...... |
........................................................... `--------------------------`---> Nitrogen Gas

The following table shows the speed of chlorine demand for each chemical and whether it forms significant CC:

Chemical . Forms CC . Chlorine Demand
CYA ............... No ....... Very Slow (roughly 2 ppm CYA per month degraded)
Biuret ............ No ....... Slow (probably hours to days similar to urea)
Allophanate .... No ........Slow (probably hours to days similar to urea)
Ammonia ....... Yes ...... Very Fast (seconds to a minute depending on CYA level)
Nitrite ............ No ....... Fast (minutes?)
Nitrate ........... No ....... None
Nitric Oxide .... Yes? ..... Fast?
Nitrous Oxide .. No? ..... None?
Nitrogen Gas ... No ...... None
 

chem geek

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I don't think it's particularly abnormal with any of those chemicals present. It just means you are at different stages of the degradation or that different types of bacteria and aerobic/anaerobic conditions are present. If you let the bacteria consume all the CYA until they are done, then you probably won't find much biuret or allophanate, but could have lots of ammonia. To get passed ammonia requires different bacteria and conditions -- both can exist in the same water at different depths.
 

Richh

New member
May 23, 2014
3
USA
I know Cl- is a pretty harsh oxidant, so would the chlorine be oxidizing the ammonia present from the bacteria into nitrite, then to nitrate, which would elevate these levels? Is there currently a way to remove nitrate from the pool without doing a drain/refill? I know there are nitrate removers for fish tanks, but they use polycaprolactone as a carbon source for the denitrifying bacteria in the tank which wouldn't (shouldn't) exist in the pool.