Cyanuric Acid

[cofive]

I came across this "Fact Sheet" that recommends that stabilized chlorine not be used in indoor spas or hottubs. http://www.dsf.health.state.pa.us/health/c...80&q=234664

The information raised a question in my mind: Does the CYA "lock" the chlorine so that it would not read as Free Chlorine in a drop test? Was wondering this since if it did affect the FC reading you could have a very high concentration of Cl with a high CYA level and appear to be a relatively low reading.

Ken

[hrustar]

Well this seems to throw a monkey wrench in the dichlor/bleach plan.

[cofive]

Well this seems to throw a monkey wrench in the dichlor/bleach plan.

Well not so much a wrench but now an additional question of is dichlor really necessary in my indoor tub or can i just start with and continue with bleach? I am still curious about the "lock" effect of CYA on testing Cl, since it may give a false low reading and attribute to what I think is a chlorine allergy reaction to my skin.

Ken

[Nitro]

Well not so much a wrench but now an additional question of is dichlor really necessary in my indoor tub or can i just start with and continue with bleach? I am still curious about the "lock" effect of CYA on testing Cl, since it may give a false low reading and attribute to what I think is a chlorine allergy reaction to my skin.

NO, you cannot just use bleach. You NEED CYA in ALL pools and spas, indoor and out, period! Without it, the Chlorine will be TOO strong.

That fact sheet has some misinformation. Chem geek can give you a detailed explination.

[quantumchromodynamics]

cofive, we are well aware of the opinions expressed in the referenced source. I believe that they are misinformed and that they do not understand the actual chemistry involved.

I believe that the science behind the recommendation to use cyanuric acid is good. Cyanuric acid provides a reservoir of chlorine that is released as the free chlorine is used.

A large part of my confidence in the science behind the recommendation to use cyanuric acid is based on Richard's research and advice. I am very certain that Richard understands the chemistry involved far better than the people who wrote that reference.

To answer your question, No, the cyanuric acid does not affect the chlorine test.

[cofive]

I'm curious, what actually causes the CYA bond to break, finally releasing the chlorine?

[chem geek]

Remember, that I am not a chemist. If you do not trust the referenced chemistry, then have someone you know who truly understands chemistry review it. It shouldn't take more than the equivalent of 1st year college chemistry, though the detailed calculations are quite tedious. Normally, today's chemists use standard chemical equilibrium programs to figure these things out, such as CHEMEQL, EQS4WIN, MINEQL+, etc., but I put everything into a spreadsheet so I and others didn't have to pay for these programs. The spreadsheet is here, though most people use The Pool Calculator to calculate dosing and the saturation index.

As for chlorine releasing from being bound to CYA, it just follows the standard laws of chemical equilibrium. The "cause" that has chlorine release from being bound to CYA is that it is constantly getting released and rebound rather quickly as is typical with many chemical reactions. For one of the reactions, half is released every 4 seconds while for another reaction half is released every 1/4 seconds; the reverse reactions are around 15 times faster (depending on FC/CYA ratio). In practice, far less needs to be released since the free chlorine doesn't generally get consumed that quickly unless someone urinates in the water. As to how much of the chlorine remains bound vs. how much remains free (as hypochlorous acid or hypochlorite ion) this is based on the equilibrium constant for the reaction (which technically is the ratio of forward and reverse reaction rate constants). Also, the chlorine gets released quickly enough from CYA that the full reserve amount (that is, both bound and unbound chlorine) gets measured in the Free Chlorine (FC) test. The FC test does not measure the "active" chlorine level. The FC would only be relevant if you were to swallow the water in which case the total chlorine capacity would be relevant in terms of the amount of chlorine consumed.

The detailed chemistry defining the chlorine/CYA relationship is described in this paper from 1973/1974. Note in particular how CYA can be seen as a hypochlorous acid (that is, "active" chlorine) buffer, holding it in reserve releasing it as the active form gets consumed. At a pH near 7.5, the dominant chemical species for chlorine bound to CYA is HClCY^- where "CY" is the core CYA ring where one nitrogen on the ring has a hydrogen, another has a chlorine, and the third has nothing which makes it a negatively charged ion (see Trichlor with 3 bound chlorine here and see CYA with three bound hydrogen here). So the following is the primary reaction that occurs which is a chemical equilibrium mostly over to the left hand side at typical FC and CYA concentrations:

HClCY^- + H₂O <<<---> H₂CY^- + HOCl

"Chlorine Bound to CYA" + Water <<<---> "CYA ion" + Hypochlorous Acid

This post goes into more details including derivation of the rough rule-of-thumb that the equivalent amount of Free Chlorine (FC) without CYA is equal to the FC/CYA ratio using their respective ppm units. This rule works reasonably well at lower pool temperatures. At hot spa temperatures of 104F, the active chlorine concentration may be 4.4 times higher than at 77F (i.e. the chemical equilibrium has a temperature dependence).

As for the Pennsylvania Fact Sheet recommendation not to use any CYA at all, this is an over-reaction to the known problems with over-stabilization, that is, using too much CYA. Though this is just a recommendation in Pennsylvania, it is a law in New York that commercial/public pools and spas not use any CYA, again, an over-reaction. If you do not use any CYA in the water at all, then at normal FC levels of 1-2 ppm or more, you are overdosing with the chlorine level. The oxidation rates will be high and this means that spa covers will degrade much faster. It is also harsher on skin, hair, and swimsuits. It also means that chlorine (hypochlorous acid) will outgas much faster as well. It also breaks down faster in sunlight, though in high bather load pools this effect isn't as noticeable since the bather load can overwhelm the chlorine loss from sunlight. Theoretically (not proven yet in any study I can find), the production of very irritating nitrogen trichloride will be higher as described in this post. In Europe, there is a German DIN 19643 standard that uses 0.3 to 0.6 ppm FC with no CYA specifically to keep the active chlorine concentration as low a possible to avoid production of certain disinfection by-products, but this technique also requires active carbon filtration which removes chlorine and chloramines so chlorine must be reinjected on each pass so is a much more expensive system. Use of CYA in the U.S. and in most residential pools in Europe is a way of achieving reasonable "active" chlorine levels while still having a "buffer" or "reserve" of chlorine readily available to handle bather load.

The Dichlor-then-bleach method provides a middle ground by effectively adjusting the spa active chlorine level (at 4 ppm FC with 30 ppm CYA) to around 0.5 ppm FC with no CYA at 104F. Almost everyone not using N2 was using Dichlor-only so clearly that would build up the CYA level much more and is the primary reason why water quality goes bad in daily-used spas after around 3 months or so. The oxidation (and sanitation) rate drops over time as the CYA level builds up and at some point is slower to oxidize bather waste than the rate at which it is introduced so such waste builds up which is one reason that can make the water cloudy. With the Dichlor-then-bleach method, the CYA only builds up during the first week and is then kept constant by switching to bleach instead (and possibly one day per month "makeup" of Dichlor). As to whether an effective 0.5 ppm FC with no CYA is sufficiently high enough to kill pathogens, take a look at this post where you can see references to numerous scientific papers describing the fairly rapid killing of pathogens with even relatively low levels of chlorine.

Many spa manufacturers say not to use bleach and the primary reason is that if you used only bleach without initial Dichlor then your spa would be too harsh on equipment and covers. Also, managing the pH requires some additional steps of having a lower TA (which is counter-intuitive) and optionally using 50 ppm Borates (e.g. Gentle Spa) because not doing that and having the pH rise too high leads to scaling. So it's just easier to tell people to just use Dichlor and then change the water more frequently. I created a table of reported hot tub itch/rash/lung reports on this forum a while back here in order to see if there was a correlation with sanitizer method. The sample is too small to be definitive, but I would say that Dichlor-only is at greater risk unless you change the water much sooner. If you use N2, then it appears that the risk may be lowered. There was hardly anyone using Dichlor-then-bleach at that time so it will take time to see if it's truly better killing the bacteria that causes hot tub itch/rash/lung as is theoretically the case. One thing is for sure: people using Dichlor-then-bleach can go far longer before changing the water in their spas and when they do so, the water isn't that refreshed meaning it wasn't that bad even after 6 months of daily use (obviously, this depends on actual bather load). That demonstrates that the oxidation rate is more consistent and able to keep up with bather load; it is presumed that the same is true for disinfection rates.

Richard

[Fungi]

I created a table of reported hot tub itch/rash/lung reports on this forum a while back here in order to see if there was a correlation with sanitizer method.

I read that post with great interest. FYI There is another source of irritation that wasn't mentioned. If you have an ozonator, they usually have a restrictor inline to keep the bubbles small. If it is removed (bad repair technician, bad...) the result is significant PH drift upwards. But it also irritated (burned) my skin! On the backs of my calves where the filter pump outlet sends a stream of ozone "bubbles". No where else was my skin irritated. But for the longest time I didn't connect the rash with the ozonator issue.

[chem geek]

Thanks for that info. Ozone is a strong oxidizer so could be irritating and normally such systems are designed to have levels of ozone that are relatively low by the time they hit the bulk spa water. With the restrictor removed, I'll bet that not only are the bubbles larger, but that the volume of ozone entering into the bulk spa water is much higher. Lots of extra bubbles would be lots more aeration, causing the pH to rise unless the TA was kept very low.

[quantumchromodynamics]

This post goes into more details including derivation of the rough rule-of-thumb that the equivalent amount of Free Chlorine (FC) without CYA is equal to the FC/CYA ratio using their respective ppm units. This rule works reasonably well at lower pool temperatures. At hot spa temperatures of 104F, the active chlorine concentration may be 4.4 times higher than at 77F (i.e. the chemical equilibrium has a temperature dependence).

Richard, do you think that adding an "Equivalent amount of Free Chlorine (FC) without CYA" calculator to the "pool calculator" would be a good idea?

[cofive]

Remember, that I am not a chemist. If you do not trust the referenced chemistry, then have someone you know who truly understands chemistry review it. It shouldn't take more than the equivalent of 1st year college chemistry, though the detailed calculations are quite tedious. Normally, today's chemists use standard chemical equilibrium programs to figure these things out, such as CHEMEQL, EQS4WIN, MINEQL+, etc., but I put everything into a spreadsheet so I and others didn't have to pay for these programs. The spreadsheet is here, though most people use The Pool Calculator to calculate dosing and the saturation index.

As for chlorine releasing from being bound to CYA, it just follows the standard laws of chemical equilibrium. The "cause" that has chlorine release from being bound to CYA is that it is constantly getting released and rebound rather quickly as is typical with many chemical reactions. For one of the reactions, half is released every 4 seconds while for another reaction half is released every 1/4 seconds; the reverse reactions are around 15 times faster (depending on FC/CYA ratio). In practice, far less needs to be released since the free chlorine doesn't generally get consumed that quickly unless someone urinates in the water. As to how much of the chlorine remains bound vs. how much remains free (as hypochlorous acid or hypochlorite ion) this is based on the equilibrium constant for the reaction (which technically is the ratio of forward and reverse reaction rate constants). Also, the chlorine gets released quickly enough from CYA that the full reserve amount (that is, both bound and unbound chlorine) gets measured in the Free Chlorine (FC) test. The FC test does not measure the "active" chlorine level. The FC would only be relevant if you were to swallow the water in which case the total chlorine capacity would be relevant in terms of the amount of chlorine consumed.

The detailed chemistry defining the chlorine/CYA relationship is described in this paper from 1973/1974. Note in particular how CYA can be seen as a hypochlorous acid (that is, "active" chlorine) buffer, holding it in reserve releasing it as the active form gets consumed. At a pH near 7.5, the dominant chemical species for chlorine bound to CYA is HClCY^- where "CY" is the core CYA ring where one nitrogen on the ring has a hydrogen, another has a chlorine, and the third has nothing which makes it a negatively charged ion (see Trichlor with 3 bound chlorine here and see CYA with three bound hydrogen here). So the following is the primary reaction that occurs which is a chemical equilibrium mostly over to the left hand side at typical FC and CYA concentrations:

HClCY^- + H₂O <<<---> H₂CY^- + HOCl

"Chlorine Bound to CYA" + Water <<<---> "CYA ion" + Hypochlorous Acid

This post goes into more details including derivation of the rough rule-of-thumb that the equivalent amount of Free Chlorine (FC) without CYA is equal to the FC/CYA ratio using their respective ppm units. This rule works reasonably well at lower pool temperatures. At hot spa temperatures of 104F, the active chlorine concentration may be 4.4 times higher than at 77F (i.e. the chemical equilibrium has a temperature dependence).

As for the Pennsylvania Fact Sheet recommendation not to use any CYA at all, this is an over-reaction to the known problems with over-stabilization, that is, using too much CYA. Though this is just a recommendation in Pennsylvania, it is a law in New York that commercial/public pools and spas not use any CYA, again, an over-reaction. If you do not use any CYA in the water at all, then at normal FC levels of 1-2 ppm or more, you are overdosing with the chlorine level. The oxidation rates will be high and this means that spa covers will degrade much faster. It is also harsher on skin, hair, and swimsuits. It also means that chlorine (hypochlorous acid) will outgas much faster as well. It also breaks down faster in sunlight, though in high bather load pools this effect isn't as noticeable since the bather load can overwhelm the chlorine loss from sunlight. Theoretically (not proven yet in any study I can find), the production of very irritating nitrogen trichloride will be higher as described in this post. In Europe, there is a German DIN 19643 standard that uses 0.3 to 0.6 ppm FC with no CYA specifically to keep the active chlorine concentration as low a possible to avoid production of certain disinfection by-products, but this technique also requires active carbon filtration which removes chlorine and chloramines so chlorine must be reinjected on each pass so is a much more expensive system. Use of CYA in the U.S. and in most residential pools in Europe is a way of achieving reasonable "active" chlorine levels while still having a "buffer" or "reserve" of chlorine readily available to handle bather load.

The Dichlor-then-bleach method provides a middle ground by effectively adjusting the spa active chlorine level (at 4 ppm FC with 30 ppm CYA) to around 0.5 ppm FC with no CYA at 104F. Almost everyone not using N2 was using Dichlor-only so clearly that would build up the CYA level much more and is the primary reason why water quality goes bad in daily-used spas after around 3 months or so. The oxidation (and sanitation) rate drops over time as the CYA level builds up and at some point is slower to oxidize bather waste than the rate at which it is introduced so such waste builds up which is one reason that can make the water cloudy. With the Dichlor-then-bleach method, the CYA only builds up during the first week and is then kept constant by switching to bleach instead (and possibly one day per month "makeup" of Dichlor). As to whether an effective 0.5 ppm FC with no CYA is sufficiently high enough to kill pathogens, take a look at this post where you can see references to numerous scientific papers describing the fairly rapid killing of pathogens with even relatively low levels of chlorine.

Many spa manufacturers say not to use bleach and the primary reason is that if you used only bleach without initial Dichlor then your spa would be too harsh on equipment and covers. Also, managing the pH requires some additional steps of having a lower TA (which is counter-intuitive) and optionally using 50 ppm Borates (e.g. Gentle Spa) because not doing that and having the pH rise too high leads to scaling. So it's just easier to tell people to just use Dichlor and then change the water more frequently. I created a table of reported hot tub itch/rash/lung reports on this forum a while back here in order to see if there was a correlation with sanitizer method. The sample is too small to be definitive, but I would say that Dichlor-only is at greater risk unless you change the water much sooner. If you use N2, then it appears that the risk may be lowered. There was hardly anyone using Dichlor-then-bleach at that time so it will take time to see if it's truly better killing the bacteria that causes hot tub itch/rash/lung as is theoretically the case. One thing is for sure: people using Dichlor-then-bleach can go far longer before changing the water in their spas and when they do so, the water isn't that refreshed meaning it wasn't that bad even after 6 months of daily use (obviously, this depends on actual bather load). That demonstrates that the oxidation rate is more consistent and able to keep up with bather load; it is presumed that the same is true for disinfection rates.

Richard

Richard, I appreciate you very thorough response. I am just an average tub owner that is trying hard to understand the information out there and am smart enough to run it by you guys for advce. If I can say without offending anyone, please guys remember some of us our just novice tub owners that are not challenging any knowledge, but instead are seeking it. Be gentle with us. Thanks again for the insight.

Ken

[chem geek]

Richard, do you think that adding an "Equivalent amount of Free Chlorine (FC) without CYA" calculator to the "pool calculator" would be a good idea?

Not really since it's not that useful a number to know. There is already a recommended FC for any given CYA level in the calculator and that implicitly is getting calculated roughly from the active chlorine level though is currently a table that is "in between" the one Ben Powell created here and the one I created here. The differences are greatest for shock levels. Ben's table was created mostly from his experience.

[chem geek]

Richard, I appreciate you very thorough response. I am just an average tub owner that is trying hard to understand the information out there and am smart enough to run it by you guys for advce. If I can say without offending anyone, please guys remember some of us our just novice tub owners that are not challenging any knowledge, but instead are seeking it. Be gentle with us. Thanks again for the insight.

Ken

Ken,

No offense taken. I never know how much info is requested (unless the request explicitly says to keep things brief and/or simple) and it's useful to have the background since more than the original poster reads these threads.

If you want to ask your pool and spa stores something, then ask them why none of the manufacturers and therefore none of these stores disclose the following chemical facts which are absolute, not controversial, cannot be refuted, and are independent of concentration of product or of water volume.

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

Richard

[aschwartz]

Well not so much a wrench but now an additional question of is dichlor really necessary in my indoor tub or can i just start with and continue with bleach? I am still curious about the "lock" effect of CYA on testing Cl, since it may give a false low reading and attribute to what I think is a chlorine allergy reaction to my skin.

NO, you cannot just use bleach. You NEED CYA in ALL pools and spas, indoor and out, period! Without it, the Chlorine will be TOO strong.

That fact sheet has some misinformation. Chem geek can give you a detailed explination.

CYA should not be used in a spa or any indoor water body. It is very much under debate for outdoor applications and is now banned in New York State commercial pools with many other states are seriously considering siginificant restrictions. At a recent water conference, it was recommended that no more than 20ppm used outdoors if at all. All the research surrounding CYA did not consider bacterial biofilm in the water. Biofilms can absorb significant amounts of Free Available Chlorine out of solution rendering it undetectable and ineffective. The bacteria biofilms grow as the water temperature increases which further reduces FAC and increases Combined Chlorine. Check out this website; http://www.erc.montana.edu/ Without understanding the effect of the biofilm on the water, one could inaccurately assume that the UV from the sun is degrading all the chlorine.

[Nitro]

CYA should not be used in a spa or any indoor water body. It is very much under debate for outdoor applications and is now banned in New York State commercial pools with many other states are seriously considering siginificant restrictions. At a recent water conference, it was recommended that no more than 20ppm used outdoors if at all. All the research surrounding CYA did not consider bacterial biofilm in the water. Biofilms can absorb significant amounts of Free Available Chlorine out of solution rendering it undetectable and ineffective. The bacteria biofilms grow as the water temperature increases which further reduces FAC and increases Combined Chlorine. Check out this website; http://www.erc.montana.edu/ Without understanding the effect of the biofilm on the water, one could inaccurately assume that the UV from the sun is degrading all the chlorine.

Allan, you are completely WRONG, and with all due respect considered a Spammer in my opinion. Your only agenda here is to sell your product, which in my opinion is nothing more than a gimmick.

You still have not answered my question. Until you do, you have no credibility whatsoever.

"The consensus here is that a properly sanitized tub will not form biofilm. Are you saying this is not true, and the only way to keep a biofilm free tub is to use your product?"

[Hillbilly Hot Tub]

I created a table of reported hot tub itch/rash/lung reports on this forum a while back here in order to see if there was a correlation with sanitizer method.

I read that post with great interest. FYI There is another source of irritation that wasn't mentioned. If you have an ozonator, they usually have a restrictor inline to keep the bubbles small. If it is removed (bad repair technician, bad...) the result is significant PH drift upwards. But it also irritated (burned) my skin! On the backs of my calves where the filter pump outlet sends a stream of ozone "bubbles". No where else was my skin irritated. But for the longest time I didn't connect the rash with the ozonator issue.

Newer, by law have to have ozone surpression. The ozone shuts off as soon as you hit any buttons. Is you tub older than 10-15 years? You should not be breathing the ozone gasses while using the tub along with the burns it can cause. Even if you are not turing your jets on, just sitting and relaing, you should hit the jets button when getting into the tub, then just shut them off. this should shut the ozone off for at least 40 minutes. Don't forget, just because there are bubbles coming out does not mean there is ozone. Sounds like all the tech did is take out the mixing chamber.

[mcw53]

Newer, by law have to have ozone surpression. The ozone shuts off as soon as you hit any buttons ...

When did this law go into effect? I've got a 2009 Hot Spring Envoy and cannot find any reference to this in the owner's manual.