CYA in Hot Tubs

[Electro]

Hi Everyone,            

I've been away for several weeks.

I have a question about cyanuric acid (CYA) buildup in the hot tub.   As many of you are doing, I have been following the Northman recommended chemistry regimen.  Results have been very good for 2 months since my hot tub was installed for use beginning July 2, 2004.

I recently read through the Taylor Test Kit book "Pool and Water Chemistry" Guide in detail. As a result, I just tested my tub's cyanuric acid (CYA) level, which of course started at zero. The regular use of dichlor, which is about 56 percent CYA, causes this stabilizer to increase regularly in the spa water, since I have very little splashout and water replacement. I had not seen any discussion about this in posts or recommendations by Northman on that other web site.

After 2 months, the CYA level is much greater than 100 ppm (I'd guess it's about 170 ppm per the test instrument). According to the Taylor Test Kit book (pages 24-25, 28, and 38), CYA has two significant downsides at levels above 80-100 ppm.  Levels above 80 to 100 are called overstabilization.  One effect is to cause chlorine to be less effective as an oxizizer and sanitizer.  The second effect is that CYA is apparently considered by unnamed goverment health agencies to be toxic above 100 ppm.  Apparently, some municipal governments specifically disallow the use of stabilized sanitizers or require CYA to be maintained below 80 ppm when they are allowed.

Based on the Taylor information, it appears my only option is to drain and refill the tub.  With levels lower than 100 ppm, the book suggests partial draining and refilling to maintain something in the 50 ppm level.  For my use, I will need to drain or partially drain and refill at least monthly in order to maintain CYA below 80 to 100 ppm.

Has anyone encountered this "problem" of high CYA and do you drain and refill much more often.  Or, do you ignore it?  Or, do you not even realize the cyanuric acid level reaches "toxic" levels in about 4-5 weeks of regular DiChlor use.  Or, perhaps you do not feel this is important to maintain the CYA below 100 ppm.

Electro

[tony]

I have also seen my CYA levels run up past 100 and I have read the info in the Taylor booklet.  I think it needs to be discussed and not ignored.

[Electro]

Tony,

Based on the lack of responses, it appears that most tub owners who use DiChlor do not realize that they are likely poisoning themselves from the buildup of cyanuric acid (CYA).  According to my calculations, after about 4-5 weeks on a regular schedule of using DiChlor, most tubs will have reached a CYA level of 100 ppm, which is considered to be toxic by health authorities.

The question is what should folks do about this.  The recommendation in the Taylor test book is to drain and refill your tub.  There is no way to neutralize or otherwise remove this stabilizer from hot tub water.

So, it appears to me that most folks using Dichlor need to drain and fill monthly, unless they are willing to subject themselves to this poison.

Electro

[bulmer4nc]

I am not sure about the CYA - we use bromine, so don't have the dichlor issue.  I will be very interested in what other people are doing - I had never thought of this.  

We are renting a house next spring (can you believe we are already booked for a beach trip that is 8 months away!?) that has a hot tub - and it will most certainly be a dicholr tub.  If this is something we need test for before allowing anyone in the tub, I sure want to know about it!

Good digging...

[stiffy]

In 1958 it was discovered that cyanuric acid would inhibit the loss of chlorine in swimming pool water due to the effects of the ultraviolet rays of the sun. When it is dissolved in water at 25 parts per million, chlorine residuals last three to five times longer than water without cyanuric acid. Therefore, using cyanuric acid as a chlorine stabilizer meant that you were able to maintain chlorine residuals more easily and economically.
The ideal and most efficient range to maintain cyanuric acid is 30 to 50 parts per million and at this level the optimum protection from ultraviolet radiation is accomplished. Levels maintained above 50 part per million were found to provide no additional advantage in chlorine protection.

The State of Florida requires pool operators to maintain cyanuric acid levels in swimming pools below 100 parts per million. In spas the level must be below 40 parts per million. Their rational is that at higher levels there is a carcinogenic (cancer) hazard that needs to be avoided.

While cyanuric acid has the afore mentioned benefits, there are also some undesirable features to it's use. In addition to the carcinogenic hazard mentioned above, there is also a significant problem with "over stabilization" that causes the chlorine to become less effective as cyanuric levels rise. In fact, at high levels of 100 parts per million and above, in addition to the violation of health department code, a dynamic process referred to as "chlorine lock' is created. This condition causes cloudiness and increased algae growth, especially diatom algae. The other problem is that cyanuric acid can only be lowered from the pool water by draining, splash-out, back washing the filter to waste or dilution from rain.

When stabilized chlorine tabs (dichlor and trichlor) are used as a sanitizer source, they contain cyanuric acid as a by-product and this is the culprit that causes the cyanuric acid to rise rapidly above the recommended levels.

Another problem with high levels of cyanuric acid is that 30% of it is measured as an alkaline component when conducting the "Total Alkalinity" test. But, this portion will have no buffering effect to pH. Because of this, with levels of cyanuric acid over 100 parts per million, the error is significant and must be deducted from the measured "Total Alkalinity" test as a correction. To overlook this correction, the test may be misinterpreted and the risk is that water may be corrosive (out of balance) without even realizing it.

When using unstabilized sodium hypochlorite (liquid chlorine) that contains no cyanuric acid, the only problem is that the cyanuric acid level tends to deplete over time due to splash-out, back washing the filter to waste or dilution from rain. Therefore, the cyanuric acid level needs to be monitored in a timely fashion and additional cyanuric acid added when the level drops below 30 parts per million.

It should be obvious from what you read above that the control of pool water balance and cyanuric acid levels can be best accomplished by using liquid chlorine as a sanitizer source

[stiffy]

http://www.kimdon.com/aquachek_green.htm
This site has test strips for CYA for $9.18

[tony]

CYA is only needed in outdoor pools where the water is in sunlight.  Indoor pools should not use stailizer or stabilized chlorines.  Portable spas, being covered most of the time, do not need stabilizer.  The reason dichlor is used is because of its neutral pH and quick dissolving characteristics.  The byproduct CYA in dichlor has not really been discussed in spa usage, but spas are not exempt from overstabilization.  I believe many feel it is not an issue because the water is changed at regular intervals, but as evidenced, CYA levels build up rather quickly, especially for those who sanitize and shock with dichlor.

[UnderTheStars]

Wow!  that's a pretty comprehensive post hd2toe!  Where did the info come from?  Are you a pool guy?  chemist?  pool inspector?  Just curious.

Oh, and thanks a lot!  One more thing I gotta test for and learn  

[Electro]

Hi Everyone:

I received a post today from Northman.  He says there is no scientific basis for either of the two concerns - (1) chlorine sanitizer is less effective at CYA above 100 ppm and (2) CYA above 100 ppm is toxic.  So, according to Northman, the Taylor test book information on cyanuric acid is based on anecdotes and rumors and is apparently wrong.

Electro

Northman's full answer is as follows:

Posted By: Northman
Date: Monday, 13 September 2004, at 10:56 a.m.
In Response To: Re: CYA Question for Northman

Ahh the CYA question. This came up about a year ago and I have been trying to research it since then. The main problem is that there is no real scientific research to date that I have been able to find, particulary in relation to spa's. I have monitored my spa now for about a year and I also went for an 8 or 9 month period with no water changes because I wanted to prove that a good scientific based spa maintenance routine can go just as long between water changes as one of the alternative enzyme routines. During that period of time my CYA readings went from 40-160ppm. I noticed no issues with chlorine becoming ineffective during this period of time. The fact the most people will top off their spa's once a month with water may have something to do with this. As far as CYA being a carcigen well that has yet to be proved as well, there is no scientific data that I'm aware to back that up as well in either a pool or spa setting. My wife had cancer so I'm very sensitive to this fact, and I aske here oncologist to do some research and he came back with nothing, so he isn't concerned. Currently while I find it a topic of interest I have decided to ignore it until sound scientific studies are available. One of the things that I have noticed with my experimentation with magnets is that because of the reduced chemical levels or the magnetic effects my CYA readings haven't gone above 50ppm for the last couple of months. Still more experimentation needs to be done here but the results so far are interesting even though they can't be explained scientificly. Bottom line is that I'm not worrying about CYA until there is more scientific studies to base that concern on, I'm more concerned about a baterial safe spa. While Tony's idea of liquid chlorine is interesting it can also cause PH problems and only has a shelf life of 3 weeks, and adds greatly to your TDS more than dichlor will. Not the definitive answer that I'm sure everyone was looking for but it is the only honest answer that I have right now. If anyone can find any scientific studies on this topic, please post them because I would like to read them.

Northman

[Oskar]

This is a post that is on Doc's forum, I don't know if this is an accepted policy on this forum and I apologize if it is not, and if it is pulled I will understand.

The following is the post.


I have never had any occasion to use this chemical except for the spa. Consequently, I know very little about it. It is a degradation product from some pesticides in addition to being an item of commerce in its own right. I looked very briefly for some studies, but like Northman, I didn't see anything terribly relevant. MSDS (Material Safety Data Sheet) info shows:
Species: Mouse
Route of Application: Skin
Dose: 138 GM/KG
Exposure Time: 2Y
Frequency: I
Result: Tumorigenic:Equivocal tumorigenic agent by RTECS
criteria. Liver:Tumors.

This means that at doses equivalent to 21 pounds of cyanuric acid applied to the skin of a 150 pound person intermittently (this often means 1x, 2x, or 3x per week) for two years (a long time in the life of a mouse), there were tumors found in the mouse BUT for one of several possible reasons, it was not possible to classify CYA definatively as "carcinogenic" or "neoplastic" according to the requirements set out in the Registry of Toxic Effects of Chemical Substances
One interesting new article indicates that some human DNA repair enzymes can repair CYA damage to DNA in contrast to the enzymes found in some bacteria which cannot repair the damage. I have no idea if this means humans are any better protected from possible tumors than mice. I think we need more studies before making conclusions. Personally, since 21 pounds of CYA in a 500 gallon tub is close to 5000 ppm, I'm not really concerned that someone needs to do the studies tomorrow to see if I'm at risk of cancer although I would very much like to see someone do such studies eventually. The benefit of keeping a microbiologically safe tub far outweighs the small possible cancer risk for me.

Starlight

If you have question about this post go to Doc's forum to ask the writer about it.

[tony]

One point I agree with is there is no scientific evidence of CYA poisoning in humans.  It is certainly true that CYA blocks the effectiveness of chlorine.  Most spas are topped off because of evaporation, unlike pools which are because of splash out and backwashing.  CYA does not diminish from evaporation.

Also, the advantages of using liquid pool shock (bleach) are no CYA and no TDS.  The only biproduct is a very small amount of salt.  Depending upon the product, the contents are anywhere from 88 to 95 percent water.  The disadvantages are very high pH (13), very short shelf life, and, if you splash or spill it, you ruin your clothes.  I have shocked with it, but only when I needed to bring my pH up.

[windsurfdog]

They can take my dichlor when they pry it from my warm, wet, sanitized, CYA laden hands!

[stiffy]

In 1958, cyanuric acid (a weak acid) also known as CYA , conditioner or stabilizer, was found to protect chlorine in pool water from ultra violet light. Losses of chlorine from pool water due to ultra violet light are extremely high. UV light degrades chlorine by a chemical reaction in which two chlorine molecules combine with two molecules of water to form four molecules of hydrochloric acid also known as muriatic acid plus oxygen. As mentioned before a chlorinated pool without CYA will lose 90% of its chlorine in just 2 hours in the sun, because of this reaction.

The mechanism by which CYA stabilizes chlorine is not known. However, the excepted theory is that hypochlorous acid (HOCl- the killing for of chlorine in water) and hypochlorite ions (OCl- -a relatively inactive form of chlorine in water) closely attach to one of the 3 free bonding sides of the CYA molecule. As long as they remain attached, they will not be degraded by sunlight. The chlorine is still readily available to work on bacteria and algae. However if there is an excess of CYA in the water (over 100 ppm) and chlorine begins to loss its ability to sanitize as it is being tied up so to speak, by the CYA. Also more importantly the health department doesn't like to see CYA go above 100 ppm as there is concern about the toxicity of cyanuric acid. While there are no known cases of cyanuric acid poisoning, health officials limit the CYA level to an upper limit of 100 ppm.

When dissolved in water at 25 ppm the free chlorine residuals would last 3-5 time longer than pool water not containing CYA. At above 50 ppm, no marginal stabilization benefit is observed. It is generally recommended that you maintain a residual of 30-50 ppm of conditioner. To obtain 50 ppm of CYA requires you to add 4 pounds of conditioner for each 10,000 gallons of water to be protected, or 1 lb./5000 gallons yields 25 ppm. Remember to avoid CYA level over 100 ppm. This commonly happens from regular addition of stabilized chlorine like Dichlor or Trichlor.

Cyanuric acid is removed from the pool water only by draining/dilution, splash out and backwashing, so it does need to be checked periodically. Usually spring and fall will do unless you use stabilized chlorine frequently then you may want to check the CYA more frequently.

[stiffy]

Some NIOSHA reports of tests..............

Available data on the hazards of cyanuric-acid (108805) is reviewed and a preliminary risk assessment is provided. The chemical identity, physical and chemical properties, means of production, and industrial uses of the compound are described. Worker, consumer, and environmental exposure are discussed. Cyanuric-acid and its chlorinated derivatives are used as chlorine stabilizers and bactericides in swimming pools. Metabolic studies are cited which show highest concentrations in the kidney, followed by blood and liver tissues. Approximately 90 percent of the administered dose is reported to be excreted in urine within 12 hours and 99 percent of this is identified as cyanuric-acid. The median lethal oral dose for rats is reported to be 5 grams per kilogram (kg). Microscopic investigation after dosing reveals atrophy of the gastric mucosa, indicating a pronounced irritating effect. Feeding studies in rats and mice suggest low tumorigenic potential. Studies of subcutaneous application in mice at an application rate of 550 to 620 milligrams/kg are reported which show no tumor induction. Dermal application of two drops of 20 percent cyanuric-acid in benzene 3 times/week to mice is reported in which two animals developed liver tumors after 22 months. Studies of teratogenic and reproductive effects of the compound in mice and rats are examined which show no dominant lethal response nor any significant difference in reproductive parameters between the experimental and control groups. Studies of the chlorinated derivatives of cyanuric-acid are also briefly reviewed. The author concludes that the lack of human epidemiological data constitutes a significant data gap, particularly with regard to persons who frequent swimming pools. Additional toxicity studies of cyanuric-acid and its chlorinated derivatives are also needed.

[stiffy]

Sodium Dichlor is produced by adding soda ash and cyanuric acid to a solution of trichlor. When dried the result is a granule that may provide 56 percent available chlorine.
note spa 56 on some containers.
PLus with ozone tubs u should not need so much dichlor.