Higher CYA levels

[Guest]

Waterbear, here is Richard's chart
pool-water-chemistry-t628.html
here he shows that the half life of free chlorine at 50ppm CYA is nearly the same as it is at 100 ppm. He says “A Little CYA Goes A Long Way” and “The following is a graph showing that a large amount of the benefit of CYA protection of chlorine from UV (sunlight) is already there at around 20 ppm”. His chart shows a logarithmically diminishing protection ending at 100ppm. It appears that his chart shows exponentially diminishing returns after 50ppm. What reference can you show to support this: "Chemtura's corperate stand is that CYA levels up to 200 ppm are acceptable for residential pools"?

I am very familiar with Richard's charts and have conversed with him at length on the subject (and others) for your information. As to Chemtura's corperate stance, just call any of their companies or look on the printout of any of their ALEX system water tests where it says acceptable CYA range is between 30-200 ppm. I have spoken to Chemtura about this BTW and they insist that CYA levels up to 200 ppm are not a problem. It is interesting that Chemtura is now incorporating borates into many of their products (in addition to pushing Optimizer and Maximizer--their brands of sodium tetraborate) because of the algaestatic properties of borates, which can help greatly when CYA levels are very high.
I personally do not advocate high CYA levels but one must take into account the climate also. In areas like Florida and Arizona higher CYA levels (up to about 80 ppm) have been found to be advatageous and the use of higher CYA levels with a SWG provide many benefits as I illustrated in this thread:
viewtopic.php?f=21&t=3663

 

[Guest]

JasonLion, it is my understanding that a cyanuric acid level over 100 would totally lock up all available chlorine and make it ineffective. Is my information incorrect?

Chlorine lock is a myth. What would happen is that there would be a greater amount of chlorinated isocyanurates present, which are not as effective as hypochlorous acid. This is why the chlorine seems to 'lock up'. However, chlorinated isocyanurates do readily release the chlorine bound to them.

 

[PoolOwnerNumber9]

To JasonLion and FrustratedPoolMom, I understand that people don’t always “want” to follow our recommendations. Sometimes you have to be insistent. Sometimes people’s objections are just testing your conviction and your confidence.

They figure that if they can talk you out of something then you must not be that sure or that it’s not that important. Part of our job as professionals is to sell people on doing the right thing. Sometimes you have to push. Sometimes it’s important not to back down. If you see someone doing something that’s not in their best interest, then it’s your obligation to say something. Of course, they don’t have to listen to you, but that’s their choice.

As to the question about a level of 300: The first thing I would do is to call a water softener company and ask them if they had a system that I could rent that would remove cyanuric acid. If not, I would drain most of the water and refill.

 

[Guest]

To JasonLion and FrustratedPoolMom, . Part of our job as professionals is to sell people on doing the right thing..

I take it by your comment that you work in the industry. In what capacity?

 

[PoolOwnerNumber9]

Waterbear, I am in service and repair. Here are two links that provide some good information on the subject.
http://www.poolspanews.com/2008/052/052acid.html
http://www.ppoa.org/pdfs/PrP_Cyanurics% ... 20Bomb.pdf

 

[PoolOwnerNumber9]

More In re: Cyanuric acid or 1,3,5-triazine-2,4,6-triol, a chemical compound with the formula (CNOH)3. A white crystalline acid, C3N3 (OH) 3. C3H3N3O3 / C3N3 (OH)3
Here is another link with some helpful information. http://www.texaswaterworks.com/overstabilization.pdf (From Arch Chemicals).

I think that it’s also important to note:
1) That about 1/3 of the cyanuric acid level should be subtracted from the Total Alkalinity. At a Cyanuric Acid level of 90, you should subtract 30ppm from your Total Alkalinity to get its true reading.
2) Cyanuric Acid levels above 50 – 70 significantly reduce the speed of the chlorine to kill certain pathogens, which increases the risk of transmission of disease.
3) ORP controllers are significantly inhibited by high levels of Cyanuric acid.
4) Plaster is damaged at high Cyanuric levels by cyanuric acid attaching to the walls.

 

[JasonLion]

JasonLion, it is my understanding that a cyanuric acid level over 100 would totally lock up all available chlorine and make it ineffective. Is my information incorrect?

This is a myth. If you raise the FC level sufficiently to compensate for the CYA level you can manage a pool with CYA up towards 200, probably even to 300-400, though it certainly isn't a good idea. Dealing with pools with CYA levels that high becomes very problematic for a variety of reasons, but "chlorine lock" isn't one of them. The main problems are that it is nearly impossible to get reliable CYA level measurements much above 100, the amounts of chlorine involved are huge particularly if there is algae, and at the required FC levels the PH tests stop working correctly.

1) Yes, CYA does affect the TA reading. For normal CYA levels we have built that effect into our recommendations. At higher CYA levels you would need to compensate manually.

2) Technically correct when the FC level is the same at low and high CYA level. By raising the FC level appropriately you can restore the kill time to what it was before.

3) ORP is essentially useless when CYA is higher than 50. Very few of the people here have ORP controllers, but for those who do lowering CYA level to 50 or lower is essential.

4) There was a report of plaster damage risks at high CYA levels, but follow up studies have been inconclusive. In my mind this is still an open issue awaiting more information.

 

[Guest]

Waterbear, I am in service and repair. Here are two links that provide some good information on the subject.
http://www.poolspanews.com/2008/052/052acid.html
http://www.ppoa.org/pdfs/PrP_Cyanurics% ... 20Bomb.pdf

I am very well familiar with the first article. Kent Williams does make some good points, such as high TDS not being a problem but rather high CYA levels (which will go hand in hand with high TDS in pools chlorinated exclusively with stabilized chlorine sources) causing problems (because the FC is too low for the CYA level) but the focus of the article is on pools controlled with ORP controllers, which is not surprising since he was formerly employed by Stranco before he started PPOA. Therefore his article could hardly be called objective. I find it very interesting that he says at the end of the article:

"This writer has, by the way, used cyanuric acid successfully
and with benefit in his own pool for years."

Here is an article Stranco wrote on CYA:
http://www.strancoaquatics.com/lit_f...ilization1.pdf
It is basically more of the same.

As far as the second article that refers to the Arch Chemical study, that study had been refuted by several sources since it could not be reproduced and because it did not take the CSI into account. Also be aware that Arch Chemical is a large manufacturer of cal hypo so they have a vested interest in pushing their cal hypo products. I find it interesting that they have discontinued dichlor for spa use in their HTH line and only sell cal hypo for spa chlorination and shocking now. In this respect they are no different then Chemtura who pushes their stabilized chlorine products and say that CYA levels up to 200 ppm are acceptable!

If you work in the industry then you know there is a wealth of misinformation and half truths that are firmly ingrained in our industry. For a case in point just look at the common belief that 'slugging' acid will lower TA while 'walking" acid will lower pH. This is blatantly untrue and and article in the JSPSI disputed this almost 15 years ago!
http://www.poolhelp.com/JSPSI_V1N2_16-30_AcidColumn.pdf
(Which is why we recommend and teach a different method for lowering TA that actually works! viewtopic.php?f=8&t=5341 )

 

[chem geek]

Re: What's an Oxidizer do?

Richard, at your chart here
pool-water-chemistry-t628.html
you show that the half life of free chlorine at 50ppm CYA is nearly the same as it is at 100 ppm. You say “A Little CYA Goes A Long Way” and “The following is a graph showing that a large amount of the benefit of CYA protection of chlorine from UV (sunlight) is already there at around 20 ppm”. Your chart shows a logarithmically diminishing protection ending at 100ppm. It appears that your chart shows exponentially diminishing returns after 50ppm.

At the beginning of the section you are referring to, I have the following Note:

NOTE: The mechanism of protection of chlorine from sunlight by CYA is currently under review in this thread. Higher CYA levels may protect even proportionately higher levels of chlorine more, especially in deeper pools.

The graphs were done BEFORE Mark's experiments and the slew of other data from pools that demonstrated that higher CYA levels in the 60-80 ppm range (especially 70+ ppm) had lower chlorine loss even at the same FC/CYA ratios. The graph was done fitting the PPOA data and other similar data using a half-life of hypochlorous acid and hypochlorite ion (50/50 mix at pH of 7.5) of 35 minutes with a half-life of the chlorinated isocyanurates (or the dominant species HClCY^-) of 8.4 hours. The problem is that this only takes into account ONE of TWO factors where CYA protects chlorine degradation. The PPOA (and my) graph only accounts for the fact that most of the chlorine is bound to CYA. It does not account for the fact that CYA itself shields lower depths of water from UV through absorption and this is absolutely, positively an effect that needs to be considered.

Also, I have since made a model of chlorine breakdown using accurate absorption spectral measurements (from here and Florida sunlight data (from here) and have a spreadsheet that actually predicts a 35 minute half-life for a 50/50 mix, but that the half-life of hypochlorous acid is 2 hours and 10 minutes while that of hypochlorite ion is 20 minutes so there is a large pH dependence that is exacerbated by having CYA in the water. This is because CYA acts as a hypochlorous acid buffer so changes in pH make rather large changes in hypochlorite ion (since hypochlorous acid doesn't change much) as shown in the graphs on the right in this post.

Data from Wojtowicz shows a roughly 14%/day drop in FC levels due to oxidation of the chlorinated isocyanurates by chlorine (actually, hypochlorite ion) that is temperature dependent (i.e. thermal decomposition). This drop is independent of sunlight and occurs day and night. So here, too, is a pH dependence where there would be faster breakdown at higher pH. Information is inconsistent, however, since Wojtowicz says that the chloroisocyanurates do not significantly absorb UV radiation in sunlight while data from O'Brien shows significant absorption of HClCY^- up to 230 nm which is as high as he measured. The UV from sunlight drops off rapidly below 320 nm and can essentially be ignored at 290 nm and below so this missing data is critical (but I can't find it anywhere). Also, the data from O'Brien shows that CYA itself does not absorb sunlight, but that HCY^-, which is the dominant species in pool water, does. In this case, higher pH provides more protection, but the increase is relatively small since most of the CYA is in the form of HCY^- already.

From the O'Brien data, it looks like the HClCY^- will have a higher molar absorptivity than HCY^- even accounting for the higher CYA concentration compared to FC (in molar terms, it's less -- around a factor of 3 when the FC is 10% of the CYA level). That would say that the CYA protection effect is even greater when the FC level is higher -- that is, raising CYA without raising FC isn't as good for this effect. One key unknown is whether the absorption of UV by HClCY^- results in its breakdown (for HOCl and OCl^- every UV photon absorbed results in its breakdown), but my guess is that it does not as the absorption may be more with the inner ring than at the N-C bond, but this is speculation on my part based on our not seeing high chlorine loss at the higher CYA levels.

So there is inconsistency in various data sources. The PPOA graph which has a fairly rapid breakdown with a half-life of 6-8 hours as a limit at high CYA is inconsistent with the fairly low loss of chlorine people experience in real pools at high CYA levels with no bather load and is also inconsistent with the Wojtowicz data. I would tend to lean towards what the O'Brien measurements of UV absorption imply followed by some of the Wojtowicz info and would regard the PPOA chart as incorrect because it is incomplete. However, even Wojtowicz says nothing about the effect we have seen which may be somewhat dependent on pool depth.

Richard

 

[chem geek]

Re: What's an Oxidizer do?

Richard, at a cyanuric acid of 80, you recommend a free chlorine of 9ppm and a shock level of 30ppm. However, due to the effect of the stabilizer reducing the reactivity of the chlorine, any test –(reagent or electronic)- will read artificially low. So, your real levels are closer to 12 and 40. Of course a cyanuric of 80 will hold the chlorine longer, but you’re getting awfully close to totally locking the chlorine up. I think that these levels are too high. I don’t like to keep the chlorine any higher than a maximum of 5 – 7 due to the negative effect on heaters and such. Like I said, I set a limit of 75ppm as a maximum for cyanuric acid. In this post the poster mentioned a cyanuric of 100 and you did not recommend any remedial action. As such, can I assume that you are OK with such a high level?

You are incorrect in assuming that the lower reactivity of chlorine will result in a lower measurement on an FC test. The FC test works by CONSUMING chlorine by having it react with a dye and measuring this intensity or by having it react with a dye and then removing (reducing) the chlorine until the sample turns clear. Either way, what FC is measuring is the chlorine CAPACITY, not its reactivity or instantaneous concentration. The reason is that chlorine gets released from chlorinated cyanurates (chlorine bound to CYA) quickly -- half gets released in 1/4 second from one species and 4 seconds from another. So in the time of the tests, all of the chlorine gets reacted. The fact that most of this chlorine was held in reserve bound to CYA doesn't affect the test.

The only tests that would be affected by the higher CYA level binding more chlorine are tests of instantaneous hypochlorous acid levels such as specialized hypochlorous acid sensors (using selective membranes) and to some extent ORP sensors though their dependence on hypochlorous acid concentration only approximately follows the theoretical Nernst equation.

When it comes to heaters, swimsuits, skin, hair, stainless steel, etc., a pool with even 40 ppm FC with 100 ppm CYA has less disinfecting and oxidizing (i.e. active) chlorine (that is, hypochlorous acid) than a pool with 1 ppm FC and no CYA. One of the hardest concepts to break in this industry is the one where they incorrectly believe that the FC measurement by itself is actually meaningful in terms of chlorine concentration or strength of effect. FC really only measures the chlorine CAPACITY or amount in RESERVE plus the active amount. When there is no CYA in the water, then at a pH of 7.5 roughly half the chlorine is in reserve as hypochlorite ion while the other half is active as hypochlorous acid. However, when there is CYA in the water, at a pH of 7.5 and 3 ppm FC with 30 ppm CYA 97% of the chlorine is bound to CYA, 1.5% is hypochlorite ion and only 1.5% is hypochlorous acid. Though the CYA reduces the hypochlorous acid instantaneous concentration and therefore its effectiveness and the rates of all reactions for which hypochlorous acid (or hypochlorite ion) participates, it does not affect the FC test. As the 1.5% of all the chlorine reacts with the dye, more hypochlorous acid is released by that bound to CYA and this continues quickly until all of the chlorine bound to CYA is released. Of course, being released quickly is not the same thing as being available immediately for determining reaction rates.

If the reaction rate of chlorine with the dye in the FC test were rate-limited and slow enough to be seen in human terms, say as many seconds to minutes at low chlorine concentrations, then you would be correct that the higher CYA level would affect the test. However, the reaction rate of chlorine with the dye is apparently very fast (I've never looked this up) so even though it is true that this rate is slowed down by roughly a factor of 100 when the CYA level is 100 compared to no CYA, it's probably changing the reaction time from something like a millisecond to 100 milliseconds (a total guess on my part) and is probably more dependent on the physical mixing rate than anything else. If the reaction rate was slower, then you should be able to see the sample getting darker over a longer period of time at higher CYA levels and with a FAS-DPD test this would end up looking like a fading endpoint. This should not be confused, however, with what happens after several minutes where a sample can get darker due to combined chlorine that also reacts with the dye, albeit much more slowly. Finally, even if there were darkening over time or a fading endpoint, this would effectively stop at some point when the change became very small and the net result is that the total capacity or reserve plus active is measured, not the "active" chlorine.

I do not recommend a CYA level of 100 ppm, but if someone wanted to have that level, they could prevent algae growth by maintaining a sufficiently high FC level of no lower than around 7 ppm (for manual dosing, with a safety factor). In fact, PoolChlor maintains pools in the very hot and sunny areas in Arizona with 100 ppm CYA and they add chlorine once a week to 14 ppm which then drops by the end of the week to around 4 ppm. The actual algae inhibition level is probably closer to 5% (assuming moderate phosphate levels < 3000 ppb) or around 5 ppm so one day at 4 ppm is not a problem for these pools. This rate of loss of FC is around 16% per day and includes some bather and organic load. It's difficult to measure 100 ppm CYA in the test and if you do get an algae bloom it takes a lot of chlorine to get rid of it, but it can be managed. Que said they only get small visible algae in perhaps a couple of pools out of over a thousand that they service and it's usually due to a late or inadequate chlorine treatment. Also, using Borates can help as an insurance policy (algaecide) as waterbear (Evan) has confirmed. On this forum, we recommend 80 ppm CYA as the highest to use, mostly for SWG pools though those in very sunny areas can do this if they desire. The Chlorine/CYA chart goes up to 100 ppm for non-SWG pools because there are situations where the CYA is that high and the pool owner can't quickly lower the CYA level.

Richard

 

[chem geek]

More In re: Cyanuric acid or 1,3,5-triazine-2,4,6-triol, a chemical compound with the formula (CNOH)3. A white crystalline acid, C3N3 (OH) 3. C3H3N3O3 / C3N3 (OH)3
Here is another link with some helpful information. http://www.texaswaterworks.com/overstabilization.pdf (From Arch Chemicals).

I think that it’s also important to note:
1) That about 1/3 of the cyanuric acid level should be subtracted from the Total Alkalinity. At a Cyanuric Acid level of 90, you should subtract 30ppm from your Total Alkalinity to get its true reading.
2) Cyanuric Acid levels above 50 – 70 significantly reduce the speed of the chlorine to kill certain pathogens, which increases the risk of transmission of disease.
3) ORP controllers are significantly inhibited by high levels of Cyanuric acid.
4) Plaster is damaged at high Cyanuric levels by cyanuric acid attaching to the walls.

I'm reiterating the points that Jason made with some more detail and references.

The above has some misinformation. First of all, the 1/3rd rule for adjusting TA for CYA is only for the purposes of the saturation index and even then this is a pH dependent adjustment where the 1/3rd rule is approximately true for a pH of 7.5.

The statement that CYA levels above 50-70 significantly reduce the speed of chlorine to kill certain pathogens is not true. The "significantly reduce" is true between having no CYA and having even a small amount of CYA such as 10 ppm. This is because going from no CYA to 10 ppm CYA with, say, 2 ppm FC increases kill times by over a factor of 10 whereas you have to go to a CYA level of 100 ppm before you get another factor of 10. So there is no large jump at 50-70 ppm and there is no scientific literature to support that. The careful studies show a roughly linear relationship with kill time vs. FC/CYA ratio that approximates hypochlorous acid concentration until this ratio gets above 0.2 (20%). There is only one study (by Adamson for algae here) that did not show an effect with CYA, but that study seems flawed as chlorine levels were not maintained (it was single low doses just above "chlorine demand" levels) and the medium used for algae food may have had ammonia in it or produced as a byproduct, hence monochloramine would be produced which would be independent of CYA level (but this is speculation on my part -- Adamson never responded to my query about this). This paper shows that it is the hypochlorous acid concentration that matters, not the FC level. This paper shows that the FC/CYA ratio is an approximate proxy for chlorine effectiveness. At a pH of 7.0 and 0.25 ppm FC, the 99% inactivation of S. faecalis for CYA levels of 0, 25, 50, 100 ppm went from 0.3, 7.2, 11.5, 21.7 minutes. The calculated hypochlorous acid concentration (from my spreadsheet) is 0.187, 0.0050, 0.0025, 0.0013 which reasonably tracks the kill times since it would predict (using 22 minutes for 100 ppm CYA): 0.15, 5.7, 11.4, 22. The error at fast kill times is probably large as the table doesn't even list it for higher chlorine levels with no CYA. This paper shows similar effects where you can see the very rapid dropoff at no CYA in terms of fast kill times. This paper is another though it only shows "<" amounts for the very fast kill rates with no CYA. There are numerous other studies as well, but I think you get the idea.

ORP controllers are not directly affected by CYA itself, but rather by the fact that the hypochlorous acid concentration is lower at the same FC when CYA is present. Some ORP controllers do not behave well at very low hypochlorous acid concentrations (low ORP values) which occurs at high CYA levels if the FC isn't raised appropriately.

The study that claims that plaster is degraded at high CYA levels is shown here, but the results of this study were not reproducible by Que Hales at PoolChlor (they have large tanks and plaster coupons) when adjusting for TA appropriately. There was no degradation and no drop in CYA level. So I consider this presumed effect questionable at best. More realistically, the industry folklore probably came from pool owners that let their CYA get high, usually from Trichlor, and their TA wasn't raised accordingly (since Trichlor is acidic, the TA would tend to drop so pool owners, at best, probably kept it constant) and the net result was a negative saturation index that resulted in plaster degradation. Whereas a pool can have a zero saturation index at 30 ppm CYA, that same pool at 200 ppm CYA (with a TA of 100) has a saturation index of -0.4 and at 250 ppm CYA it's -0.6 and at 300 ppm CYA it's -1.34 (and very dependent on TA -- at a TA of 120 ppm the saturation index is -0.55).

Richard