Help me please with my cya problem

[manistyman]

Richard:

Thank you for your gracious response.

Yes, salt and sugar do have high solubility, whereas cyanuric acid does not. This, combined with its weight, led me to suggest that CYA might have the ability to settle in water -- perhaps in still, uncirculating water and over time.

Just a theory.

Thanks again.

[chem geek]

I see where you were going, but a lower solubility doesn't mean something will be a suspension vs. full dissolved. The solubility of CYA is around 2000 ppm so much higher than what is found in pools. The slow dissolving of pure CYA is also misleading since the slowness is partly due to the acid being weak. There is a fast dissolving salt of CYA in a product called Instant Pool Water Conditioner that is about twice as expensive as pure CYA, but dissolves readily in water. The primary chemical species in pool water near pH 7.5 is cyanurate ion where one of the hydrogen attached to CYA has been dissociated. This is why the sodium salt of CYA dissolves more quickly since the sodium is removed from the CYA readily, leaving a cyanurate ion. Also, Dichlor dissolves quickly as well, though this adds chlorine in addition to CYA.

[apsi pools]

There is a new product on market which reduces CYA via pulls it out of solution hitting floor. you must vacuum once reaction occurs or staining would occur..

[chem geek]

Do you have a link to this product? I believe it's just melamine and would create a cloudy mess that takes a while to remove (some would precipitate to the floor perhaps aided by a built-in flocculant). This is similar to what is done in the CYA test itself except that's done at low pH to cause more to precipitate. One couldn't lower the CYA to lower than 30 ppm using melamine in pool water, but that's not bad were it not for the mess. Also, when one tried to increase CYA, it would continue to cloud up again though wouldn't drop quite as much.

Is this what you are talking about? It is no longer available. Or is it this?

[CWMike]

There is reference to a reagent that can reduce CYA ... good read. http://www.ppoa.org/pdfs/PrP_Cyanurics% ... 20Bomb.pdf

[chem geek]

Yes, I'm familiar with that article and it refers to melamine, which is what I said in my post, in reducing CYA. However, at pool pH, melamine cyanurate is soluble to around 20-30 ppm so you can't lower the CYA below that amount without using a lot of excess melamine. Don't forget that melamine is what was put in pet food in China to look like more protein in measurements and caused cats and dogs to die when melamine cyanurate crystals formed in the kidneys. It's not likely to be something generally allowed in pools anymore, though I don't know for sure.

By the way, the article was written by Kent Williams who worked in the ORP industry so had biases there. For example, he says to never use CYA in indoor pools because there is no sunlight there, but he doesn't say to only use 0.2 ppm FC in those environments so instead having more typical 1-2 ppm FC with no CYA is over-chlorinating such pools and likely leads to much higher nitrogen trichloride concentrations. He's got all the information about CYA's moderating influence on chlorine strength, but then he goes the other extreme for indoor pools.

Maybe he just left out how they should operate with low FC, similar to the German DIN standard (0.2 to 0.6 ppm FC with no CYA) though that might be hard to control and not run out of chlorine capacity under local bather load (though the Europeans don't seem to worry about that). He's dead on, however, in his ranking of chlorine requirements and how most pathogens are easy-to-kill (especially killing them faster than they can reproduce) so the higher active chlorine (hypochlorous acid) levels that lead to higher ORP are really needed for killing algae and oxidation of bather waste, though the extra chlorine level also provides further protection for harder-to-kill pathogens and for faster killing to prevent possible person-to-person transmission of disease.

I just think there needs to be some balance and for commercial/public pools that's possibly around an FC that is 20% of the CYA level for an effective 0.2 ppm FC with no CYA equivalent while in residential pools the lowest would be around 5-10% of the CYA level mostly to prevent algae growth (since bather loads are low).

[kluke]

I agree...fire the pool company -- THEY are the problem.

[Me...]

Chemgeek. I think its generally accepted that you do not use CYA on an indoor pool. Well unless it salt I guess but that is the SWG manufacturers I believe. On a residential indoor pool you could probably get away with low chlorine residuals because the demand would typically be so low. Commercially they need all the impact they can get because of the demands. Health Board will mandate around 1.5ppm but no matter what levels they maintain they should be upping them if they continue building chloramines. If they use CYA indoors this will simply cripple the chlorines ability to oxidize. I continually see commercial/public pools running combined up near 1ppm or more while trying to maintain a 1.5 - 2ppm FC.

Now, I need to check something hopefully today. I just heard of a pool with a TC of about 7.5. FC was about 3.5 and this indoor commercial pool has CYA in it, about 100ppm I think it was. Apparently because the local authority wants it in there. And of course the pool is a mess with a pH over 8.

[chem geek]

Yes I know the general rule in the industry is to not use CYA in indoor pools and obviously using too much, such as 100 ppm, is going to slow down oxidation too much and build up monochloramine and dichloramine (and chlorourea). The interesting thing about the chemistry, however, is that lower active chlorine levels result in lower nitrogen trichloride being produced and that's the worst offender for smell and irritation though obviously having too much monochloramine and dichloramine isn't good either.

The German DIN 19643 standard used in Europe has the FC between 0.3 and 0.6 ppm in order to reduce disinfection by-products. The standard also uses activated carbon to remove chloramines during filtration, but that also removes chlorine that must be added back.

What I am proposing is 4 ppm FC with 20 ppm CYA which would be technically equivalent to 0.2 ppm FC with no CYA. It is true that this lower level will have chlorine react more slowly, but it should also significantly lower the nitrogen trichloride production, but at the sacrifice of higher intermediate monochloramine and dichloramine levels. Based on the odor detection limits for these, there is a balance that can potentially be achieved. At a higher FC with no CYA, such as 1-2 ppm, the chlorine is at least 5-20 times stronger and that means faster oxidation of swimsuits, skin and hair as well as faster rates of corrosion (especially in salt pools as you mentioned). However, it is nitrogen trichloride that is the primary factor of concern and that is theoretically proportional in amount to the active chlorine (hypochlorous acid) level at the same bather load.

Most of the chloramine that is being measured in a DPD test is likely to be chlorourea since urea is the largest component of sweat and urine and takes longer to oxidize. This doesn't appear to be particularly volatile so the DPD chloramine measurement is giving a reading of chlorourea, an organic chloramine, and secondarily that of monochloramine (dichloramine is much lower in concentration and nitrogen trichloride is too low to measure in DPD). Work being done by Dr. Ernest "Chip" Blatchley (here and here) seems to show this false interference in the DPD test.

It's definitely too early to propose a sweeping change, but I'd like more research done in this area and unfortunately current research into disinfection by-products, especially with indoor pools, is not considering CYA as a factor at all, in spite of the fundamental known chemistry showing how much the disinfection by-products change at different active chlorine levels. I suspect there is a sweet spot at a lower active chlorine level. If an indoor pool were able to consistently maintain 0.2 ppm FC with no CYA, then that would be another way to handle this, but if that is too difficult to achieve because of local bather load and imperfect circulation, then having 4 ppm FC with 20 ppm CYA would be another way to achieve something similar.

There also needs to be research in other ways of dealing with combined chlorines. The German DIN 19643 is one approach, but others may include supplemental oxidation (UV or ozone) or the use of selective enzymes, especially for urea/chlorourea and other components of sweat and urine.

We had one residential indoor pool owner who had persistent chloramines and even with bucket tests hitting with high FC without CYA they would not get lowered in any reasonable period of time (we tried it both ways -- with and without CYA and at different FC levels and even tried adding some ammonia to produce some intermediates). So more chlorine isn't always the answer and, as noted above, it can have side effects of higher nitrogen trichloride production. Ultimately, the user got a UV system and that did result in a lowering of measured CCs. Basically, the disinfection by-product production is a function of the bather load and all that chlorine can do at different levels is change the species of what is ultimately produced, but at the end of the day you will still get some forms of disinfection by-products. By using a lower active chlorine level, you can at least lower the nitrogen trichloride at the expense of monochloramine and dichloramine. More research is needed to see what happens to THMs (i.e. chloroform) and other by-products.

Richard

[Me...]

I see your theory but in fact I like to see higher free chlorine than .2ppm anyways. That is the level the books and common sense dictates would be max for combined chlorine. Theory would also dictate 2ppm free residual to be able to combat the combined, at least following the rules of superchlorination.

Another reason to use something like 1 to 1.5ppm FC would be to keep from using too much chlorine. In a pool free of organics, algae and bacteria for instance would there not be less chlorine consumption than maintaining 4ppm? If so there would be less need to adjust the pH, and therefore the Alkalinity? And in a pool with all the contaminants I would think you would want a much more potent level than .2ppm. Which you indicate would be the equivalent of 4ppm with CYA added.

It seems pools than run 1.5ppm free with no CYA tend to run into plenty of problems related to low chlorine as it is. Although you obviously know your chemistry I would still expect to see all kinds of issues with a less potent chlorine level. As you say, lots of testing would be required.

[chem geek]

If there really were problems with low active chlorine levels, you'd see them in outdoor pools that typically have CYA and sometimes have low FC/CYA ratios with effective FC of less than 0.1 ppm if there were no CYA. So at a minimum, there is a big inconsistency. Indoor pools have 5-20 times the active chlorine concentration due to the lack of CYA compared to outdoor pools. That's pretty extreme.

FC is just a capacity or measure of chlorine reserve, not of chlorine strength. The active chlorine (hypochlorous acid) level is proportional to the FC/CYA ratio -- when the FC is around 10% of the CYA level at a pH near 7.5, this is roughly equivalent to 0.1 ppm FC with no CYA.

[Me...]

I think you do see these problems in outdoor pools. Water is generally a bit cloudier and usually has more debris which itself will increase demand. In an outdoor pool however you are not recycling the air. People will not notice the odors and irritations of the indoor pools because of the fresh air. Air movement over the water itself would help any offgassing also which should go a long way to removing the gas pocket over the water you can find on an indoor pool.

I see problems in all pools and I wish they would all keep their chlorine higher whether they have CYA or not. If I come across a pool with combined chlorine in it, it needs to have a higher FC residual. Of course they need to keep everything else in line too.

[chem geek]

But that is the irony. It is true that if one has too little chlorine and a high bather load then one can build up monochloramine which is typical "pool smell". However, if one has too much chlorine, specifically hypochlorous acid as with an FC with no CYA, then one can produce more nitrogen trichloride which is very irritating at low concentrations and is very volatile. So there is a balance between these. Anyway, further study is needed and what would work better for a lower bather load situation is not necessarily the approach for a higher bather load situation. I just suspect that even hitting a decent balance for a high-bather load situation is going to need further supplemental oxidation no matter what. If one tries to do that with higher active chlorine levels, then one can produce more irritating nitrogen trichloride. pH also is a big factor here where lower pH products more nitrogen trichloride.

Though having a higher chlorine level will tend to lower the steady-state combined chlorine (CC) reading, the bulk of the CC reading may be chlorourea which could be fairly innocuous. Do you find in the pools with high CC readings that they are consistently more smelly or offensive? Sometimes this would certainly occur such as when the CC were monochloramine, but if the CC were mostly chlorourea then it might not be odorous.

[Me...]

High CC is pretty much always a dead give a way because of odors. Especially in pools where the aeration is on/off. When the air starts in places such as tots pools and hot tubs the gas cloud is usually quite offensive. I swim a lot and if I am in a pool that starts aerating I habitually move away from that area.

Also I find in those pools the pH is off because of the high chlorine consumption. Whatever form the chlorine takes the pH heads steadily in that direction. These pools will next get cloudy and probably start foaming because the water balance gets so bad and the chlorine is too weak to even start oxidizing organics. Hotel pools because noone is ever around to monitor them and the only "automation" they have is a puck feeder with 20 pucks or none in it or something ridiculous like that. Public pools because the bather loads come at night and the night operators quite often are not allowed to treat the water or are not trained to.

If it could be proved CYA actually did help in an indoor pool it might then be only in lower loaded pools. And someone would have to write a rule on that. You seem to have a great knowledge of chemistry and I now pretty much take you at your word on most things. But I still rarely see public or commercial pools that are in balance consistently and when you do they are pretty obvious and as far as I know the authority does not allow CYA in them. I'm rambling LOL

[chem geek]

Not rambling...great info! Well, we'll just have to see from more studies what makes sense. Unfortunately what we mostly have right now are the two extremes: no CYA at all which produces high nitrogen trichloride vs. high CYA from Trichlor chlorinators which produces high monochloramine (and chlorourea). Both of these extremes are problems. There's not much in that controlled middle to know if that might be something better.

Thanks again for keeping it real.