CYA and water chemistry questions

[IN DEPTH]

Yeah, we have only been doing this since around 2007.

We are Chevy dealers and you think we should espouse Fords and Hondas?.......not interested. sorry.

All dealerships are required by law to sell other manufacturer's vehicles.

Yeah, I've been doing this successfully for just as long as TFP.

Y'all are very coarse people.

I'm not debating anything. I'm only looking for smart people that know about things that I am interested in. Usually smart people are tolerant of questions because that's how things grow and get better.

If you don't have anything positive to contribute, feel free to not respond. Understand.

 

[IN DEPTH]

Not if you adjust the FC level to the CYA, always keeping FC/CYA constant. Deactivation times correlate with HOCl, not FC.

For example:

View attachment 513768


From:

Chlorinated Cyanurates: Review of Water Chemistry and Associated Drinking Water Implications

Since 1958, cyanuric acid and two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid), have been added to outdoor swimming pools ...

www.ncbi.nlm.nih.gov

Or:
View attachment 513769


From:

Assessing the Impact of Cyanuric Acid on Bather’s Risk of Gastrointestinal Illness at Swimming Pools

Current regulatory codes for swimming pool disinfection separately regulate free chlorine (FC) and cyanuric acid (CYA). It is well-known that CYA affects disinfection rates by reversibly binding to FC in aqueous solutions. However, limits for these regulated parameters have neither...

www.mdpi.com

Exactly!

However, FC can be consumed faster than it is added where CYA remains relatively constant (or increasing if using a trichlor tab feeder).

 

[IN DEPTH]

TFP's recommendations, particularly at the Pool School Article level, are targeted to be easy to understand for the average pool owner who's pool turned green. TFP gives easy to understand guidelines that work.

We encourage SWGs, because they are the easiest and most convenient way to chlorinate a pool. And over the lifetime of the cell also the most cost effective. Especially with the recent inflation of chlorine prices.

I honestly have no experience with chlorine dosing systems. But I consider them - at least in a residential environment - as not as reliable as a SWG. Mostly, because you are depending on the strength of the chlorine to be consistent. From batch to batch, but also degradation within one reservoir fill. You can argue that you can compensate for varying chlorine strength by adjusting dosing with automated ORP testing. Unfortunately, ORP doesn't really work in the presence of CYA, so it is not really compatible with the TFP method (and I consider automation an optional add-on, rather than a requirement for the TFP method). And I don't think that maintaining a residential backyard pool without CYA is a good idea. Then you need to keep the chlorine reservoir filled. I consider the risk of something with a chlorine dosing system to go wrong higher than with an SWG.

TFP gives the average residential backyard pool owner a method that works, and that makes pool maintenance easy and affordable. The website is designed to teach this method (the TFP method, not another method) to pool owners who ran into trouble, not for the expert.

More information can be found in the wiki articles or in the Deep End. Chem Geek's sticky threads provide a lot of extra information and background details. Many questions that I had when I started here I got answered by the forum search. Or by asking questions like you do right now.

Once the principles of the method have been understood, there is nothing wrong in testing the boundaries. Feel free to run your own tests and trials and report your results back. Maybe you can help to develop our recommendations.

I up to speed on the TFP method and I'm not challenging it.

I'm seeing holes in the recommendation to run high CYA with saltwater pools. That's it.

It's not even that TFP recommends running high CYA (and I think that's why I am being met with derogatory comments from admins and members - which is completely uncalled for, disrespectful and unprofessional).

The manufacturer's of SWCGs are recommending higher CYA.

I am familiar with most sanitation methods and hardware as well as supplemental methods and hardware. There's a lot of really cool stuff out there!

What I find is that moderation is best. Find the minimums per situation and maintain.

 

[IN DEPTH]

Not if you adjust the FC level to the CYA, always keeping FC/CYA constant. Deactivation times correlate with HOCl, not FC.

For example:

View attachment 513768


From:

Chlorinated Cyanurates: Review of Water Chemistry and Associated Drinking Water Implications

Since 1958, cyanuric acid and two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid), have been added to outdoor swimming pools ...

www.ncbi.nlm.nih.gov

Or:
View attachment 513769


From:

Assessing the Impact of Cyanuric Acid on Bather’s Risk of Gastrointestinal Illness at Swimming Pools

Current regulatory codes for swimming pool disinfection separately regulate free chlorine (FC) and cyanuric acid (CYA). It is well-known that CYA affects disinfection rates by reversibly binding to FC in aqueous solutions. However, limits for these regulated parameters have neither...

www.mdpi.com

I really like the Assessing the Impact of Cyanuric Acid on Bather’s Risk of Gastrointestinal Illness at Swimming Pools article. I've read it before and it affirms my position.

I am constrained by local health codes, however.

There are A LOT of commercial pools that rely on large trichlor tab feeders. Increasing the output of the feeder increases FC, but CYA also increases.

 

[IN DEPTH]

Every other method of chlorine addition is a rapid spike of FC. Then it has 24 hours slowly drift down. The only exception is chlorine tabs, but they are released into the water with CYA which gives the FC a head start to build.

The SWG needs the protection.


Now. With overwhelming members experiences agreeing, if it wasn't for the threat of SLAM, we would likely reccomend all members run at SWG levels.

But LC people don't need to assume that risk like SWG people do, so their level remains particularly on the low side of most effective UV protection. However, in several hot climates, members will go to 60 to overcome the brutal sun, which effectively puts them at low SWG level.

*******So there you have it. You're right. They should both be one level, the SWG level.******

The science will never factor the downsides of what to do if there is an algae bloom. Life happens to all of us and the pool takes a back seat if a family member is in ICU (etc etc etc). Or because lazy. Or because confused newb. So we factor that into our equations on the LC side.

Now, that make sense and without too much condescension and

Every other method of chlorine addition is a rapid spike of FC. Then it has 24 hours slowly drift down. The only exception is chlorine tabs, but they are released into the water with CYA which gives the FC a head start to build.

The SWG needs the protection.


Now. With overwhelming members experiences agreeing, if it wasn't for the threat of SLAM, we would likely reccomend all members run at SWG levels.

But LC people don't need to assume that risk like SWG people do, so their level remains particularly on the low side of most effective UV protection. However, in several hot climates, members will go to 60 to overcome the brutal sun, which effectively puts them at low SWG level.

*******So there you have it. You're right. They should both be one level, the SWG level.******

The science will never factor the downsides of what to do if there is an algae bloom. Life happens to all of us and the pool takes a back seat if a family member is in ICU (etc etc etc). Or because lazy. Or because confused newb. So we factor that into our equations on the LC side.

Now, that make sense and without too much sanctimonious condescension.

Again, I am not arguing the feed rates of SWCGs or manually dosing with bleach or injecting bleach with a metering pump.

I am arguing for moderation. High CYA can be laborious to deal with when life happens. It seems like a trap to me.

A 60ppm CYA requires a minimum of 4.5ppm FC to avoid issues.

I'm conscientiously trying apply TPF resources and knowledge base to public swimming pools (*where I can and where practical). Most residential pools don't have the exposure that commercial pools get and probably don't need the fastest possible CT times. I have been tasked with protecting the public from communicable disease in recreational water. I am merely looking for a thought provoking discussion. Please, by all means continue to enjoy the TFP method. Y'all do like to bite though.

 

[IN DEPTH]

What would you have done differently? What would you consider a control sample? No exposure to the sun?

The test was meant to be a simple comparison of FC loss with different CYA levels at the same CYA/FC ratio.

Also, I have run this test multiple times in multiple containers (pool, spa, bucket, glass). In every case, higher CYA results in lower UV extinction (i.e. lower absolute FC loss). But if you don't believe me, then run tests yourself.

To me, the last test I did is the most definitive and the easiest to replicate since it requires very little solution. It is a dilution test that keeps the FC/CYA ratios the same by diluting the solution with distilled water so as not to add anything other than water. All three test samples were performed at exactly the same time so there were no sun exposure differences.

But again, if you have a better method of testing, please do so then post the results.

It's not that I don't believe you or that CYA does what it's purported to do.

mgtfp shared scholarly articles recently. When reading those, anyone will find a sense of professionalism that is beyond reproach. However, even those studies are scrutinized by peers.

 

[mgtfp]

The association of chlorine with CYA is governed by reversible reactions, such that as unbound chlorine is used, more is released. As a result of these equilibria, CYA functions as a free chlorine buffer. However, binding of chlorine to CYA reduces the concentration of the most biocidal form of chlorine, hypochlorous acid (HOCl), and increases the time required to inactivate microbial pathogens.

Defined concentrations of chlorine and CYA will result in a well defined concentration of HOCl, that can be calculated with the O'Brien model (or measured with more advanced techniques that are no longer residential pool owner compatible). The involved equilibrium reactions are very fast (which is also the reason why chlorinated cyanurates show up as FC in tests). If you have 0.5ppm HOCl in the water then you have a certain kill time, the kill time is not affected by chlorinated CYA that is also in the water.

Lets take a simple example. Lets assume you have pool without CYA with FC 1ppm at pH 7.5, then you will have an HOCl of 0.5ppm. These 0.5ppm define the pathogen deactivation rate. Lets say you have an amount of pathogens that requires 0.5ppm of HOCl to kill. This means that FC got reduced to 0.5ppm, and while this was happening the equilibrium reactions ensured that we end up with HOCl 0.25 ppm (and OCl- 0.25ppm). From this point on, the deactivation rates will be determined by this value, and your kill times have basically doubled now.

Now we assume a situation where we have the same 0.5ppm of HOCl in the water with CYA of 50. This requires an FC of about 25.3ppm at pH 7.5 (this shows how strong 1ppm without CYA actually is). A nice side effect of CYA is that at pH 8, we'd still have 0.42ppm of HOCl, but in the above case without CYA, we'd only have 0.24ppm HOCl at FC 1 and pH 8. But that's not my point. Lets assume the same amount of pathogens eats up 0.5ppm of HOCl. This happens initially at exactly the same kill rate as above. After FC reduction of 0.5ppm to 24.8ppm, we now still have an HOCl concentration of 0.48ppm. Our HOCl has only been reduced by 4% rather than being halved as in above case. You will hardly notice a change in kill rates from this point forward. That's how the chlorine buffering effect of CYA works.

This has been calculated with the Pool Equations spreadsheet that I have posted earlier.

Exactly!

However, FC can be consumed faster than it is added where CYA remains relatively constant (or increasing if using a trichlor tab feeder).

The same as just explained applies here as well.


The point I wanted to make is that FC and CYI should not be considered independent parameters. Of course, if you keep FC constant and increase CYA, then the pathogen kill time creeps up.

TFP recognises the FC-CYA equilibrium chemistry, and applies it into a method designed for maintenance of residential backyard (outdoor) pools. The FC level needs to be adjusted to the CYA level. In a residential setting, we are not limited to regulated FC and CYA boundaries, and can run a pool with CYA 90 at FC 10 or 12 to ensure that there is sufficient HOCl available. And we discourage usage of chlorinated cyanurates for regular chlorination to avoid escalating CYA levels. The method's aim is to enable simple, affordable pool maintenance. Following the method, there should never be a reason to drain a pool, unless there are other factors like fill water that is high in calcium and/or metals that accumulate over time.

The method is not designed to be compatible with typical methods of companies servicing residential pools. Having trichlor tabs permanently floating in a pool with weekly shock doses, as typically applied to serviced pools without SWGs or chlorine dosing systems, is not compatible with the TFP method.

The aim of the Falk paper was to highlight the importance of the FC/CYA ratio for pool sanitation, and suggest that regulations (applicable for public pools) should recognise that. Rather than regulating FC and CYA independently, they should be regulated together. In many legislations you are currently allowed to run a pool for example at FC 1ppm and CYA 100ppm, which is not great in terms of pathogen kill times.

One solution is to ban CYA altogether (which by the way would not just limit the use of chlorinated Cyanurates, but completely ban them). And this can be a legitimate solution. But in this case FC should be limited to lower values. To swim in FC 4ppm without CYA is not a pleasant experience.

The other option is to allow CYA, but limit the CYA/FC ratio (or, equivalently, specify a minimum FC/CYA ratio). Falk's paper suggests, I'd say, a compromise that would not be too disruptive within the current framework of regulations. One of these framework regulations is that FC is usually limit to values like 4ppm. By suggesting a max CYA/FC of 20 (equivalent to a min FC/CYA of 5%), this effectively limits the max CYA level to 80ppm. This limits (but not eliminates as suggested by you) considerate use of products like Trichlor or Dichlor.

It's not even that TFP recommends running high CYA (and I think that's why I am being met with derogatory comments from admins and members - which is completely uncalled for, disrespectful and unprofessional).

The manufacturer's of SWCGs are recommending higher CYA.

Depends what you consider high. TFP recommends with SWGs CYA up to 80. Some in very hot, sunny climates go even up to 90ppm. With manually chlorinated pools, we recommend more like 40-50ppm.

It's not that I don't believe you or that CYA does what it purported to do.

You shared scholarly articles recently. When reading those, anyone will find a sense of professionalism that is beyond reproach. However, even those studies are scrutinized by peers.

We are all residential pool owners here. We have day time jobs and families to look after. There is not much peer reviewed literature available that shows experiments on CYA concentration effects on FC protection. We have seen in our own pools, confirmed by many members at TFP, that higher CYA provides better protection. But this is more anecdotal evidence, rather than peer reviewed "proof", I get that. Tests like the ones conducted by mas985 have the purpose to quantify this anecdotal evidence better. But it hasn't been through a peer review process, that is correct.

If you have the means to conduct more thorough testing on FC protection by CYA at higher levels and publish it in a peer reviewed journal, then we would be thankful for this.

Other aspects, like the importance of HOCl rather than FC for pathogen deactivation times or the FC/HOCl ratio as a proxy for HOCl, are well covered by peer reviewed literature. We give recommendations on required FC/CYA ratios that work, keep a pool sanitised, algae free and not overchlorinated (contrary to many public pools operating for example at FC 4 with CYA 0). This is the main aspect of TFPC. Which CYA level you chose for a pool, is in the end not that critical, as long as you chose the right FC, and are able to never drop below a critical threshold. TFP gives recommendations that work based on the experience of TFP members, but in the end it is up to the individual to pick what works for them.

 

[newdude]

I am arguing for moderation. High CYA can be laborious to deal with when life happens. It seems like a trap to me.

Again. I am agreeing with you, free of condescension.

Your point is the exact quandary and the reason for 2 levels.

When things are good, the higher CYA is the way to go.

When things are bad, you'll wish you had lower levels.

Warmer climates need more CYA either way. The further north you go, the lower they need. But most fall into the 30(LC) /70(SWG) categories found from years of fine tuning the science.

 

[SoDel]

I'm conscientiously trying apply TPF resources and knowledge base to public swimming pools (*where I can and where practical). Most residential pools don't have the exposure that commercial pools get and probably don't need the fastest possible CT times. I have been tasked with protecting the public from communicable disease in recreational water. I am merely looking for a thought provoking discussion. Please, by all means continue to enjoy the TFP method. Y'all do like to bite though.

Lively and very interesting discussion. For public pools governed by various regulations and regulators, there are plenty of studies for HOCL levels that render acceptable CT for sanitation. ChemGeek’s sheets based on O’Brien’s equilibriums will let you calculate the resulting HOCL from any reasonable FC & CYA so it’s relatively easy to “pick your poison” in a reasoned way. In that context, the science seems simple enough. Levels are generally checked frequently as mandated by regulations and if done right, risk is within some acceptable range, greater than zero, but very low as determined “acceptable” by some whatever factor of just life has risks, so other than making public pools impossible, health experts can pick a number that can be lived with.

In a residential pool, it’s reasonable to think that it should be basically the same, minus the regulatory constraints. But the difference I think generally folks don’t go swimming in their own pool when ill, folks don’t generally test their water and maintain as close tolerances as is required for public pools, and there is no widespread risk to the public. So it becomes what’s really practical and works, with a foundation in the science but with a very heavy dose of practicalities and long and wide breadth of experience. I understand the desire for a better answer but I don’t think there is one.

 

[duraleigh]

Good post, SoDel.

 

[mgtfp]

I would love to put more scientifically sound evidence behind CYA recommendations and the best possible FC for a CYA. But who's going to run the required tests? The industry won't be interested. At TFP, we are in the end just pool owners who want to use their pools. Find an FC/CYA that works and move on. We give recommendations that are a good starting point to wiggle into one's personal sweet spot.

I'm not interested in finding the absolute min FC that's required to keep algae away. Because that means that I have to cross the border, and then deal with the algae. No interest.

Some people accidentally cross the border. By reporting back here, we build up anecdotal evidence, which we can use to give recommendations.

And even if we worked out what the perfect CYA is. What do we do with it? Create a huge table based on lattitude, maritime climate vs continental climate, etc? What do we do in an El Niño or a La Niña year? I don't think that's worth it.

And yes. If you chose to run higher CYA, you need to be extra vigilant in staying above the minimum. Clearing algae at CYA 80 is not fun. It's never fun, actually, but even worse when having to drain half the pool first.

That's why we encourage a higher target FC range. I think that a higher CYA will help to stay clear of the critical min FC as long as you chose a suitable target FC range. You have a much larger CYA range where you're FC will be protected. Especially in hot, arid climates CYA degrades over time. In wet climates you wash it out with rain overflow. The lower you start, the sooner you are below that 20-30 range where UV protection really crashes. Ideally, you'd realise this by testing before you are not able to maintain FC beyond noon.

But again, we give advice to home owners how to run a trouble free pool. We are not a public pools with hourly or even continues testing, that you needed to run close to the absolute minimum.

We encourage newbies to start with daily testing of FC and pH until you get a feeling for your pool. Once you have that feeling, and once the novelty of testing had worn off, most drop down in test frequency. We have lives and just want fun and safe pools for our families and friends to enjoy. We don't want to tell people that they need the XL CYA reagent bottle and test CYA daily and FC hourly to be able stay at the absolute minimum FC.

We tell people to pick a CYA that works based on our experience base, and run FC high enough to have enough wiggle room to not drop too low. Ever. With a reasonable testing regime. Accept that with an SWG your FC will wander up sometimes when it's cloudy for a week. That's fine. By the time you realise this, you are still below SLAM, which in terms of HOCl is way lower than what you are exposed to in many public pools.

I personally prefer my SWG pool to run at liquid chlorine FC targets. But I chose a higher CYA of 70-80. That works for me to keep my pool trouble free.

Again, the corner stone, the importance of the FC-CYA relationship, is scientifically sound and well documented in the literature. A higher CYA requires higher FC to ensure sufficient deactivation times.

We give advice to residential pool owners/users. The pool industry is welcome to join, learn, give feedback, discuss, use the method within applicable boundaries. But that's not our target audience.

 

[duraleigh]

Another good post,mgtfp. You clearly define our purpose and you define how we got here and where we are going!

 

[Pauls234]

Well, I was going to add some comments but then read SoDel and mgtfp posts and realized I would only echo their thoughts in a less articulate way.

TFP is perhaps the friendliest community on the internet, and this thread is pretty good evidence.

Suggestions otherwise strike me as projection.

 

[IN DEPTH]

Lively and very interesting discussion. For public pools governed by various regulations and regulators, there are plenty of studies for HOCL levels that render acceptable CT for sanitation. ChemGeek’s sheets based on O’Brien’s equilibriums will let you calculate the resulting HOCL from any reasonable FC & CYA so it’s relatively easy to “pick your poison” in a reasoned way. In that context, the science seems simple enough. Levels are generally checked frequently as mandated by regulations and if done right, risk is within some acceptable range, greater than zero, but very low as determined “acceptable” by some whatever factor of just life has risks, so other than making public pools impossible, health experts can pick a number that can be lived with.

In a residential pool, it’s reasonable to think that it should be basically the same, minus the regulatory constraints. But the difference I think generally folks don’t go swimming in their own pool when ill, folks don’t generally test their water and maintain as close tolerances as is required for public pools, and there is no widespread risk to the public. So it becomes what’s really practical and works, with a foundation in the science but with a very heavy dose of practicalities and long and wide breadth of experience. I understand the desire for a better answer but I don’t think there is one.

Absolutely! That’s what my experience had shown.

Example of what I am dealing with:
I have one seven (7) day per week commercial pool right now:
• 80,000 gallons
• 1200 - 1800 gallons of water loss per day
• fill line timed for 1.5 hours in 15 minutes increments every day
• Random bather load from 0 to 50 plus
• Two Rainbow 300-29X chlorinators (fits roughly 20 trichlor tabs when they stack properly)
• pH regulated - 7.0 to 7.8
• FC regulated - 1.0 to 8.0ppm
• CYA regulated - 0ppm to 80ppm
• Pool is open 7 days per week from sun up to sun down
• Board has asked to minimize water use and prevent shutdown due to high FC and/or high CYA and/or low pH

I'm doing my best to maintain a 1ppm to 3ppm daily with night additions of cal-hypo.
I have left CYA to build via chlorinator use from 30ppm. I am fully charging the chlorinators every three days.
At fully charged on a weekday, I leave them both at half output and increase each day after until wide open on Friday and weekends.
I also add sodium carbonate for pH management and sodium bicarbonate to help with natural pH rise.
The chlorinators barely keep up with demand on weekends fully charged and wide open.
I tend to catch the water just under 1ppm FC.

There was over 80ppm CYA (tough to mark a test at that level) at the beginning of the season; however, the pool was covered (not winterized) and quite green opening. *This is my first season with this pool.
There was a 3" Fernco fitting and Oatey two-part epoxy under it on one inlet of a Triton II. The backwash line was terminated 6" into a sump that's too small to contain the 5HP flow on backwash. I reduced the water level in the pool several times to reduce the CYA to 30ppm and dilute the algae while repairing the rigged plumbing. I then super'd to kill the algae, brushed extensively and vac'd to waste using my Superflo VS service pump and firehose combo (I say that b/c I am quite proud of the rig).
Any changes to plumbing and/or sanitation plan/design must be approved by DHEC.

CYA is now at about 35-45ppm depending on when it's tested. Testing during the day yields a higher result.
DHEC test results tend to be comparable to my test results, but they aren't a match. For example, my pH of 7.4 is a 7.0 with DEHEC. Regardless of the reasons why, I have to stay within range and compensate for testing tolerances.

I tend to visit this pool after-hours in order to add a bit of cal-hypo and soda ash and test for any combined that could cause issues. The result is a quite turbid pool for a couple days and filter pressure that rises 5 to 8 psi over those days. The plumbing is still quite janky. There are several filer inlet/outlet adapter collars that are cracked and allowing a bit of leaking. Hence, any filter pressures over 10psi gives me the willies. There were a couple compression fittings that slid off during a backwash when the filters were at 25psi with high pressure leakage at the air purge lid. The result was water rocket that spun filter one (three 600# filters in tandem) about 30 degrees which sheared off the inlet/outlet adapters and threw the pumps (*tandem 2.5HP Super Pumps) about 20 degrees and two feet.

I target a 5.0-6.0 FC and a pH of 7.4. If target any higher on either, the water will become opaque.

I have suggested a complete re-working of the plumbing and filter situation as well as a bleach (12%) injection system or ChlorKing lease. The board is content with me dealing with it manually, obviously.

Risk management is why I opt for moderation.

I guess I could raise the CYA to 60ppm and maintain above a 4.5ppm FC. I'm just concerned about falling below that minimum, needing to shock and then dilute to reopen.

Basically, it's just make it happen in the best way that we can!

Defined concentrations of chlorine and CYA will result in a well defined concentration of HOCl, that can be calculated with the O'Brien model (or measured with more advanced techniques that are no longer residential pool owner compatible). The involved equilibrium reactions are very fast (which is also the reason why chlorinated cyanurates show up as FC in tests). If you have 0.5ppm HOCl in the water then you have a certain kill time, the kill time is not affected by chlorinated CYA that is also in the water.

Lets take a simple example. Lets assume you have pool without CYA with FC 1ppm at pH 7.5, then you will have an HOCl of 0.5ppm. These 0.5ppm define the pathogen deactivation rate. Lets say you have an amount of pathogens that requires 0.5ppm of HOCl to kill. This means that FC got reduced to 0.5ppm, and while this was happening the equilibrium reactions ensured that we end up with HOCl 0.25 ppm (and OCl- 0.25ppm). From this point on, the deactivation rates will be determined by this value, and your kill times have basically doubled now.

Now we assume a situation where we have the same 0.5ppm of HOCl in the water with CYA of 50. This requires an FC of about 25.3ppm at pH 7.5 (this shows how strong 1ppm without CYA actually is). A nice side effect of CYA is that at pH 8, we'd still have 0.42ppm of HOCl, but in the above case without CYA, we'd only have 0.24ppm HOCl at FC 1 and pH 8. But that's not my point. Lets assume the same amount of pathogens eats up 0.5ppm of HOCl. This happens initially at exactly the same kill rate as above. After FC reduction of 0.5ppm to 24.8ppm, we now still have an HOCl concentration of 0.48ppm. Our HOCl has only been reduced by 4% rather than being halved as in above case. You will hardly notice a change in kill rates from this point forward. That's how the chlorine buffering effect of CYA works.

This has been calculated with the Pool Equations spreadsheet that I have posted earlier.



The same as just explained applies here as well.


The point I wanted to make is that FC and CYI should not be considered independent parameters. Of course, if you keep FC constant and increase CYA, then the pathogen kill time creeps up.

TFP recognises the FC-CYA equilibrium chemistry, and applies it into a method designed for maintenance of residential backyard (outdoor) pools. The FC level needs to be adjusted to the CYA level. In a residential setting, we are not limited to regulated FC and CYA boundaries, and can run a pool with CYA 90 at FC 10 or 12 to ensure that there is sufficient HOCl available. And we discourage usage of chlorinated cyanurates for regular chlorination to avoid escalating CYA levels. The method's aim is to enable simple, affordable pool maintenance. Following the method, there should never be a reason to drain a pool, unless there are other factors like fill water that is high in calcium and/or metals that accumulate over time.

The method is not designed to be compatible with typical methods of companies servicing residential pools. Having trichlor tabs permanently floating in a pool with weekly shock doses, as typically applied to serviced pools without SWGs or chlorine dosing systems, is not compatible with the TFP method.

The aim of the Falk paper was to highlight the importance of the FC/CYA ratio for pool sanitation, and suggest that regulations (applicable for public pools) should recognise that. Rather than regulating FC and CYA independently, they should be regulated together. In many legislations you are currently allowed to run a pool for example at FC 1ppm and CYA 100ppm, which is not great in terms of pathogen kill times.

One solution is to ban CYA altogether (which by the way would not just limit the use of chlorinated Cyanurates, but completely ban them). And this can be a legitimate solution. But in this case FC should be limited to lower values. To swim in FC 4ppm without CYA is not a pleasant experience.

The other option is to allow CYA, but limit the CYA/FC ratio (or, equivalently, specify a minimum FC/CYA ratio). Falk's paper suggests, I'd say, a compromise that would not be too disruptive within the current framework of regulations. One of these framework regulations is that FC is usually limit to values like 4ppm. By suggesting a max CYA/FC of 20 (equivalent to a min FC/CYA of 5%), this effectively limits the max CYA level to 80ppm. This limits (but not eliminates as suggested by you) considerate use of products like Trichlor or Dichlor.




Depends what you consider high. TFP recommends with SWGs CYA up to 80. Some in very hot, sunny climates go even up to 90ppm. With manually chlorinated pools, we recommend more like 40-50ppm.



We are all residential pool owners here. We have day time jobs and families to look after. There is not much peer reviewed literature available that shows experiments on CYA concentration effects on FC protection. We have seen in our own pools, confirmed by many members at TFP, that higher CYA provides better protection. But this is more anecdotal evidence, rather than peer reviewed "proof", I get that. Tests like the ones conducted by mas985 have the purpose to quantify this anecdotal evidence better. But it hasn't been through a peer review process, that is correct.

If you have the means to conduct more thorough testing on FC protection by CYA at higher levels and publish it in a peer reviewed journal, then we would be thankful for this.

Other aspects, like the importance of HOCl rather than FC for pathogen deactivation times or the FC/HOCl ratio as a proxy for HOCl, are well covered by peer reviewed literature. We give recommendations on required FC/CYA ratios that work, keep a pool sanitised, algae free and not overchlorinated (contrary to many public pools operating for example at FC 4 with CYA 0). This is the main aspect of TFPC. Which CYA level you chose for a pool, is in the end not that critical, as long as you chose the right FC, and are able to never drop below a critical threshold. TFP gives recommendations that work based on the experience of TFP members, but in the end it is up to the individual to pick what works for them.

 

[IN DEPTH]

Again. I am agreeing with you, free of condescension.

Your point is the exact quandary and the reason for 2 levels.

When things are good, the higher CYA is the way to go.

When things are bad, you'll wish you had lower levels.

Warmer climates need more CYA either way. The further north you go, the lower they need. But most fall into the 30(LC) /70(SWG) categories found from years of fine tuning the science.

I think we are vibing! I appreciate the support from across the aisle!

I have 60% saltwater pools. None are above 40ppm CYA. I live in Augusta, Ga. It's 92ºF right now. I get a 1ppm at times, but usually around 2ppm or slightly more. The runtimes vary and I tend to leave the runtimes alone b/c of spillovers and water features etc that are preferential to the owners. I try to run 8 hour or less filter runtimes and 50% to 60% cell runtimes. I have one client that runs three sheer descents for 10 hours a day and circulates the pool only when running the Polaris for two hours. I have mentioned that this may not be the best idea. This is why I point most of my clients to TFP, but there's a reason they called me in the first place.

I really try to run minimums and test and treat in small doses.

 

[IN DEPTH]

I would love to put more scientifically sound evidence behind CYA recommendations and the best possible FC for a CYA. But who's going to run the required tests? The industry won't be interested. At TFP, we are in the end just pool owners who want to use their pools. Find an FC/CYA that works and move on. We give recommendations that are a good starting point to wiggle into one's personal sweet spot.

I'm not interested in finding the absolute min FC that's required to keep algae away. Because that means that I have to cross the border, and then deal with the algae. No interest.

Some people accidentally cross the border. By reporting back here, we build up anecdotal evidence, which we can use to give recommendations.

And even if we worked out what the perfect CYA is. What do we do with it? Create a huge table based on lattitude, maritime climate vs continental climate, etc? What do we do in an El Niño or a La Niña year? I don't think that's worth it.

And yes. If you chose to run higher CYA, you need to be extra vigilant in staying above the minimum. Clearing algae at CYA 80 is not fun. It's never fun, actually, but even worse when having to drain half the pool first.

That's why we encourage a higher target FC range. I think that a higher CYA will help to stay clear of the critical min FC as long as you chose a suitable target FC range. You have a much larger CYA range where you're FC will be protected. Especially in hot, arid climates CYA degrades over time. In wet climates you wash it out with rain overflow. The lower you start, the sooner you are below that 20-30 range where UV protection really crashes. Ideally, you'd realise this by testing before you are not able to maintain FC beyond noon.

But again, we give advice to home owners how to run a trouble free pool. We are not a public pools with hourly or even continues testing, that you needed to run close to the absolute minimum.

We encourage newbies to start with daily testing of FC and pH until you get a feeling for your pool. Once you have that feeling, and once the novelty of testing had worn off, most drop down in test frequency. We have lives and just want fun and safe pools for our families and friends to enjoy. We don't want to tell people that they need the XL CYA reagent bottle and test CYA daily and FC hourly to be able stay at the absolute minimum FC.

We tell people to pick a CYA that works based on our experience base, and run FC high enough to have enough wiggle room to not drop too low. Ever. With a reasonable testing regime. Accept that with an SWG your FC will wander up sometimes when it's cloudy for a week. That's fine. By the time you realise this, you are still below SLAM, which in terms of HOCl is way lower than what you are exposed to in many public pools.

I personally prefer my SWG pool to run at liquid chlorine FC targets. But I chose a higher CYA of 70-80. That works for me to keep my pool trouble free.

Again, the corner stone, the importance of the FC-CYA relationship, is scientifically sound and well documented in the literature. A higher CYA requires higher FC to ensure sufficient deactivation times.

We give advice to residential pool owners/users. The pool industry is welcome to join, learn, give feedback, discuss, use the method within applicable boundaries. But that's not our target audience.

I understand completely.

I am developing a program to train my future techs and this is where I start. I am not looking for y'all to accommodate my trade, only muse with me on best practices.

I always try to run minimums on equipment (to clarify a recent comment). I definitely need a good bit of wiggle room with FC! Just trying to do the best for my clients on all fronts: water, equipment and cost.

Maybe I should draft up an agreement that includes running higher CYA with the contingency that the client agrees to maintain the salt cell every three months, replace it immediately when it dies or be prepared to drain half the pool water. The solution is having a plan and being transparent on what it takes to get to a goal.

 

[mas985]

L

mgtfp shared scholarly articles recently. When reading those, anyone will find a sense of professionalism that is beyond reproach. However, even those studies are scrutinized by peers.

A quick search reveals less than 10% of all research is peer reviewed. Some cite less than 5%. So are you sure those particular studies were actually peer reviewed? Citations don't count. But in general, I do not doubt the results of these studies only the applicability to a particular pool's chemistry and environment.

I have 60% saltwater pools. None are above 40ppm CYA. I live in Augusta, Ga. It's 92ºF right now.

That means more SWG cells that you can sell your clients so good for you.

I have a different priority and have had a pool for going on 18 years now with a SWG. I target a CYA of 80 ppm but in some years after the rainy season, the CYA level drops significantly. When I compare FC levels the week before and after adding CYA to get back to get back to 80 ppm, FC of course goes up which is to be expected. But it goes up more than the CYA went up on a percent basis so the resulting CYA/FC ratio goes down which means I can reduce the SWG setting and extend the life of the SWG which is my priority. This is consistent with the other testing that I have done outside of the pool.

 

[IN DEPTH]

Well, I was going to add some comments but then read SoDel and mgtfp posts and realized I would only echo their thoughts in a less articulate way.

TFP is perhaps the friendliest community on the internet, and this thread is pretty good evidence.

Suggestions otherwise strike me as projection.

Yeah, we have only been doing this since around 2007.

We are Chevy dealers and you think we should espouse Fords and Hondas?.......not interested. sorry.

I was just looking for a discussion on the merits and pitfalls of higher CYA concentrations.

Instead of either starting a discussion or being directed to some other source, I received several repetitive posts on pool water maintenance in a highfalutin tone.

I was a bit protracted in the beginning, granted. I asked about the chemical mechanism that supplies HOCL from chlorinated cyanurates.

My though process was that typical residential SWCGs (like the Intellichor series, TurboCell series, Autopilot series, Aquapure series) produce a relatively small amount of chlorine and to support a higher CYA concentration there would have to be a higher FC. With varying loads on water and sunlight exposure, most of these salt cells may have trouble keeping up with higher CYA/FC ratios without supplement. As I tell my clients, it's really not that difficult. I'll find out what works for your pool and keep it there while trying to target minimums (runtimes and FC with room to move).

The scenario I try to avoid is high CYA with pools that are in distress. Something like a pump failing half way into the weekly service cycle, electrical outage, cell inspection timer reached, cell end of life reached, filter occlusion, etc etc. I can pivot to manual dosing very quickly and keep the pool water maintained while simultaneously fixing other issues.

You have realize that I am dealing with a lot of swimming pools and I need to incorporate risk management. I'm not poolside everyday or most days like homeowners or TFPers. However, y'all have some really sharp folks here that I enjoy chatting with. In that same vein, it's quite well known that TFPers are rather quick to defend the methodology.

I was not, in any way, trying to question the TFP method (which I find odd that I have to even mention). I was asking about the chemistry around CYA. There's a lot of points and counterpoints out there and there's regulations that prevent me from using all the tools available because of the lack of understanding/confusion/firewalls in the industry.

Specifically, the ratio between CYA and FC is crucial and is exactly what mgtfp eloquently and articulately posted. However, most regulations are based on recommendations by the alphabet people which regulate CYA and FC independently.

Regulators assume that pool operators are stupid and need things to be super simple (I guess they think a ratio is over our heads), but then you have a pool with 100ppm CYA and 1ppm FC.

The limits in South Carolina: 1ppm to 8ppm for FC and 0ppm to 80ppm CYA. There's a ton of combinations in there!

However, I can't run higher CYA without breaking the limit on FC when maintaining a proper ratio. I think regulators also want to ensure that FC is not ever at hazardous level regardless of CYA even though CYA buffers its potential. This buffering is the crux of my question. How the concentration of HOCL is modulated via equilibrium reactions. Basically, at certain CYA:FC there's a certain amount of HOCL which is maintained almost instantly until the FC runs out. If the FC is consistently being supplemented by a feeder or whatever at a rate that does't break the ratio, then everything is hunky dory. This can get a bit hairy without knowing the body of water and equipment well.

And because there is no barrier to entry in the pool industry, it is assumed that we are mostly uneducated morons wielding a cal-hypo scooper or a jug of bleach. In a lot of cases, this is very true. Most pool pros around here overdose pools to keep them clear, but as mgtfp said swimming in 4ppm is not great; well think about 10ppm with 15ppm CYA and you'll get an idea of what a lot of pool techs tend to do. Why? They are seasonal workers and it's easier to drop 2 pounds of cal-hypo into a skimmer.

99% of my clients are high-net-worth and completely hands-off. Y'all are doing exactly what I tried to do in the beginning of my business which is "teaching a man to fish." My clients don't wanna fish; they want to pay.

 

[IN DEPTH]

L

A quick search reveals less than 10% of all research is peer reviewed. Some cite less than 5%. So are you sure those particular studies were actually peer reviewed? Citations don't count. But in general, I do not doubt the results of these studies only the applicability to a particular pool's chemistry and environment.


That means more SWG cells that you can sell your clients so good for you.

I have a different priority and have had a pool for going on 18 years now with a SWG. I target a CYA of 80 ppm but in some years after the rainy season, the CYA level drops significantly. When I compare FC levels the week before and after adding CYA to get back to get back to 80 ppm, FC of course goes up which is to be expected. But it goes up more than the CYA went up on a percent basis so the resulting CYA/FC ratio goes down which means I can reduce the SWG setting and extend the life of the SWG which is my priority. This is consistent with the other testing that I have done outside of the pool.

Exactly!

I would much prefer to do exactly what you are doing!

I really do try to extend the life of equipment to the best of my ability.

I also have to hedge for clients running a heater at 88ºF with air temps at 80ºF, hosting the kindergarten class of 2023, and leaving a slide running all day.

My clients are raw consumers.

 

[mgtfp]

One crucial difference between residential pools and commercial pools is bather load.

One consequence of that is a different risk scenario in regards to disease transmission. In the backyard pool you have better control over sick people not going in the pool. And if someone's sick in the family, they will likely spread the joy anyway, I don't have to go into the pool to catch my kids' gastro. I am more worried about algae in my pool than catching my son's gastro. But I know that by keeping it algae free the TFP way, it will also be sanitary.

Another consequence is different main sources of chlorine demand. In a residential pool with low bather load, UV is usually the main chlorine eater, that puts a much higher focus on CYA levels.

In a high bather load commercial pool, the contribution of UV on chlorine demand is in a completely different ratio to loss due to bather waste. The buffering effect of CYA can still be of benefit, but what we consider the optimum CYA for a residential pool, may not be the optimum for a commercial pool.

SWGs are great for backyard pools, but in commercial pools you need to deal with varying bather loads and sudden spikes in chlorine demand. That puts other methods like automated liquid chlorine dosing or chlorine gas injection into a different focus.