CYA and water chemistry questions

[mgtfp]

The equilibrium is skewed heavily enough to reverse the reaction to HOCL production and exhaust the FC within the same time frame as water with little to no CYA (with only demand as a catalyst).

What’s the equilibrium constant between species? I get that it’s dynamic, but it’s gotta have something that induces a move/change/delta and also solves for an increase in CT and oxidation/sanitation effectiveness.

There's nothing skewed, it's all just plain old equilibriums. The more CYA, the higher the proportion of chlorinated Cyanurates and the less HOCl, therefore higher total FC required to have sufficient HOCl to do the work. If some HOCl gets "used" by killing or oxidising stuff or by UV, then the proportions of HOCl and chlorinated Cyanurates reshuffle very quickly to the new FC. I find the term "release" of HOCl a bit oversimplified and it can be misleading.

It's not just one equilibrium, there are a couple of them which lead to a system of equations that need simultaneous solving which requires numerical methods.

You can find the complete set of equilibrium reactions/equations together with the equilibrium constants in O'Brien's paper:

https://www.troublefreepool.com/~richardfalk/pool/OBrien.pdf

Chem Geek had put together a spreadsheet that he used to solve the involved equations and to do all the calculations he is referring to in his sticky threads in the Deep End (I highly recommend to go through them). You can find the spreadsheet here:

https://www.troublefreepool.com/~richardfalk/pool/PoolEquations.xls

I’m curious about less UV causing a stacking effect. I’m wondering if less UV not only reduces less FC but also retards the reaction between chlorine and CYA? In other words, is it a photo-reactive reaction?

I was more interested in the photo-reactivity of the reaction. Is UV not a contributing factor? It may not be and the shielding effect is purely a positive side-effect.

UV contributes in the sense that it leads to a quick decay of OCl- into Cl-, but the chlorinated Cyanurates are well protected from this decay. The equilibriums between CYA, HOCl and OCl- themselves are not UV dependent. But it influences the system by "removing" OCl- (and also some HOCl, but the UV induced HOCl decay is much slower than OCl- decay, so most of the HOCl gets lost via the indirect path of OCl- being lost and some HOCl then turning into OCl- to re-establish the equilibrium between the two, which is then susceptible to UV decay).

Experience has shown that the higher the CYA, the better the UV protection effect at identical FC/CYA ratios (which would result in identical HOCl and OCl- levels). Why this is so, we haven't fully understood. Chem Geek discussed this extensively in his chemistry thread. But that's why we recommend higher CYA levels with SWGs to make use of this effect while being at low risk of having to SLAM. We don't recommend these higher CYA levels for liquid chlorine pools, because the risk of having to SLAM is higher. And SLAMing at CYA 80 usually requires draining to reduce CYA first.

Some energy is released from the system as nitrogen and some chloride reforms with sodium to return to salt. The process repeats.

There is no recombination of Sodium and Chloride in water happening. When NaCl dissolves in water it separates inti Na+ and Cl- ions, and they remain separated. When we measure "salt" in the pool, we technically only measure the Cl- content. This Cl- could come from various sources, like added NaCl-salt, added CaCl2-salt, added chlorine (via liquid, Di-/Trichlor or Cal-Hypo, the chlorine in all these sources all ends up eventually as Cl-) or muriatic acid (which is hydrochloric acid or HCl which dissociates completely into H+ and Cl- when added to water).

While in water, the Na+ and Cl- ions remain dissociated, the sodium ions are just hanging around, having no direct involvement in all the chlorine reactions going on.

With a SWG, the Cl- ions are eventually "recycled" into FC, but otherwise the Cl- ions also just hang around with no further direct involvement in the reactions.

 

[IN DEPTH]

Experience has shown that the higher the CYA, the better the UV protection effect at identical FC/CYA ratios (which would result in identical HOCl and OCl- levels). Why this is so, we haven't fully understood. Chem Geek discussed this extensively in his chemistry thread. But that's why we recommend higher CYA levels with SWGs to make use of this effect while being at low risk of having to SLAM. We don't recommend these higher CYA levels for liquid chlorine pools, because the risk of having to SLAM is higher. And SLAMing at CYA 80 usually requires draining to reduce CYA first.

I read Chem Geek’s thread and is why posted!

I really appreciate you taking the time to reply!

I’m not trying to argue with the results of higher CYA in SWCG pools; however, it completely breaks with the FC to CYA ratio and w/o much explanation of why.

That’s what I’m driving at by asking the technical questions. I want to understand why.

How is sodium hypochlorite so different than SWCG? Isn’t HOCL produced by both? Why would a SWCG pool not need to be superchlorinated or supplemented?

Have a birthday party with 10 kids in 22k gallons over four hours or more and a salt pool will need a bit of added chlorine afterwards (as my experience has shown). There’s zero FC after a swim meet at a 200k gallon commercial pool with ChlorKing 25 pound SWCG set to hold 3ppm with 60 CYA. This is after a full day of recreational use.

It seems to me that FC is proportional to use and feed rate.

There is no recombination of Sodium and Chloride in water happening.

I guess what I meant was that chloride (CL-) is used to produce chlorine (CL2) via electrolysis. Doesn’t CL2 produce CL-?

 

[newdude]

How is sodium hypochlorite so different than SWCG

In the end it isn't. It's just a matter of whether you add it or the SWG does for you.

But the SWG adds slooooowly so it's not a good way to boost the FC when low. Instead, jack it immediately away from min with LC, then let the SWG maintain the target level.

Why would a SWCG pool not need to be superchlorinated or supplemented?

With proper monitoring, neither a SWG pool or a LC pool need over correcting with shock or superchlorinate.
A party, or busy public pool day, needs extra either way to get through the higher bather load.

Have a birthday party with 10 kids in 22k gallons over four hours or more and a salt pool will need a bit of added chlorine afterwards (as my experience has shown).

We recommend starting higher, to fall back into target range. I recently had a party expecting 25 kids in 34k gallons. I aimed for 20FC before, plenty below my SLAM level of 28, and I finished in the mid teens. They could have used more or less and either way I was covered.

There’s zero FC after a swim meet at a 200k gallon commercial pool with ChlorKing 25 pound SWCG set to hold 3ppm with 60 CYA. This is after a full day of recreational use.

Commercial bather loads are their own rodeo.

 

[IN DEPTH]

In the end it isn't. It's just a matter of whether you add it or the SWG does for you.

But the SWG adds slooooowly so it's not a good way to boost the FC when low. Instead, jack it immediately away from min with LC, then let the SWG maintain the target level.

With proper monitoring, neither a SWG pool or a LC pool need over correcting with shock or superchlorinate.
A party, or busy public pool day, needs extra either way to get through the higher bather load.

We recommend starting higher, to fall back into target range. I recently had a party expecting 25 kids in 34k gallons. I aimed for 20FC before, plenty below my SLAM level of 28, and I finished in the mid teens. They could have used more or less and either way I was covered.

Commercial bather loads are their own rodeo.

I’m here swimming in the deep end b/c I totally understand more than the basics. I’m asking about real deal chemistry. I’m not licking my finger to find the direction of the wind.

I have a degree in math and a lot of hours in advanced chemistry, engineering and computer science. I’m not a chemist or an engineer, but I can follow the science.

I totally get the production rate of SWCGs across the line. I’ve installed quite a few of them from Pentair, Hayward and Jandy to ChlorKing. I’ve installed quite few variable and fixed rate Stenner pumps for bleach systems.

The Trichlor tab feeder is ubiquitous to most commercial pools in my area. Residential pools are 50/50, salt or no feeder of any kind (tabs in the skimmer, *ugh*).

I’ve been doing the pool thing for a living for around 15 years with a few other ventures in between. I’ve been quite successful.

My main query and the intended focus of discussion is the contrast in recommended concentrations of CYA between saltwater pools and any other means of chlorination.

Scientists at NIST, NIOSH, CMAHC and the CDC have told me that CYA in excess of 40ppm has shown to be of no benefit.

However, I get a lot of dancing around the chemistry when I ask why (regarding high or low concentration).

So why 60-80ppm for SWCGs? What’s the science behind a higher concentration?

Q: What happens when the cell reaches end of life or hits an inspect cell at 500 hours or gets crusted with calcium?
A: The production of FC decreases or ceases. If the pool is managed by a pool tech once weekly, there’s probably going to be a water quality issue that will be difficult to correct with high CYA.

**Not every pool is a TFP pool, but I do agree with the approach. Pool techs and pool maintenance businesses aren’t going anywhere any time soon, so we might as well work together.**

The FC/CYA ratio recommended for SWCG compared to the FC/CYA ratio recommended for anything else makes saltwater pools vastly different (on paper).

CYA does help a lot, but 60-80ppm is really high and, in my opinion, asking for problems. Orenda scientists and lots of other smart folks agree on this.

There is at least one state that has banned CYA.

Chloramines happen. People wee in pools and chlorine does become combined. Superchlorination of public swimming pools is inevitable. If it’s not happening, then you have a gross situation.

The Department of Health (DHEC) regulates the free chlorine concentration in public swimming pools. The maximum FC allowed in South Carolina to remain open to bathers is 8ppm (regardless of CYA concentration).

It seems like there’s a lot of whatever around the CYA topic and it gets irritating.

I would really like to see an open forum discussion that addresses anecdotal evidence and prescriptions with applied science.

 

[newdude]

Scientists at NIST, NIOSH, CMAHC and the CDC have told me that CYA in excess of 40ppm has shown to be of no benefit.

The scientific chart often pointed to claims 50 is the sweet spot with very little gained above that. But that's in a lab with fixed UV. In the real world, Arizona and Buffalo have drastically different UV indexes and we've had thousands of data points to compare. (We'd have 360k but not every member shares their experience)

@dfwnoob pointed it out a couple weeks ago that with enough data points, we then become the science.

So why 60-80ppm for SWCGs? What’s the science behind a higher concentration?

In a 25k gallon pool 1 gallon of 10% is 4ppm, or a reasonable peak season daily loss. If spread over 24 hours like a SWG could produce it, it would be like adding one drop every .876 seconds. Said drop would never amount to anything when UV loss was factored in. It would be burned off before it dispersed across the pool. So the higher CYA allows it to build faster than it burns off in the 60/80 range (Buffalo/Phoenix). OR. The SWG would need to be run at a higher % to overcome this, effectively shortening its life. This is the true motive as SWGs are expensive. I could probably run mine 100% with a 40 CYA and maintain target range in NY. But I'd lose 40% or more of its life.

Obviously at night the SWG is all gain. We are starting to see modern problems where people run the SWG only at night to save on electricity, and the pool is effectively a LC pool that swings normally during the day, just with a higher CYA and slightly less daily loss because of it.

Again, thousands of members have taught us this. Thousands and thousands have used it and agreed. We started where the science pointed and fine tuned it further. Science does not study us or our methods. Maybe one day.

Q: What happens when the cell reaches end of life or hits an inspect cell at 500 hours or gets crusted with calcium?

Or a dozen other things that might stop FC production for a day or days. We reccomend daily checks and anyone who strays does so knowing that it will be on them when the SLAM has a much higher target than a LC pool.

**Not every pool is a TFP pool, but I do agree with the approach. Pool techs and pool maintenance businesses aren’t going anywhere any time soon, so we might as well work together.**

They just don't mix. There are GREAT service people out there. If the customer is only willing to pay for once a week, said service persons hands are tied. Then there's the bad apples that every group has. Then there's the rest of them who mean well, but have been misled by the industry reps who taught them a method designed to sell overpriced products. Bioguard does not want me to have a cheap and easy pool. If they did they'd sell me baking soda as baking soda, and only when I needed it. They want to fleece me for every penny they can.

We can work with you personally. We can learn from each other at times and agree to disagree at others like civilized adults. But the industry and TFP are simply on 2 totally different paths.

As far as reconciling how a 200k commercial pool would respond to TFPC, it's simply not compatable. TFPC was never going to be for commercial applications. We are a residential based method.

There is at least one state that has banned CYA.

TFP is politics free so I am unable to comment on legislature. I will say that neither side is happy and we can all agree with that.

 

[mgtfp]

Scientists at NIST, NIOSH, CMAHC and the CDC have told me that CYA in excess of 40ppm has shown to be of no benefit.

However, I get a lot of dancing around the chemistry when I ask why (regarding high or low concentration).

So why 60-80ppm for SWCGs? What’s the science behind a higher concentration?

Our experience here has shown, that higher CYA does provide better UV protection. If you've read through Chem Geek's chemistry sticky, you will have seen him mentioning that a number of times, but you will also have seen him admitting that he doesn't fully understand why this is the case, suggesting some ideas. Just going by the percentage of chlorine that is attached to CYA (calculated with the O'Brien model), doesn't deliver this effect. That's where those statements like "beyond 40ppm gives no additional protection" come from.

But we have seen again and again that there is an effect beyond 40ppm. mas985 for example has done extensive testing over the years to quantify this. Here his latest results:

Many years ago, I did a test of chlorine loss vs CYA level and published the results here:

CYA Testing Update

I thought I would give those who are interested an update on some testing that I have been doing regarding CYA levels and chlorine. First a summary of the testing that I did in this thread. - Running my spa with the SWG at CYA levels from 45-80 ppm showed no change in chlorine production. -...

www.troublefreepool.com

There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now.

This time around, I wanted to use distilled water for dilution to avoid adding anything into the water that might affect the results. Also, for this round, I wanted to use shallow containers (wine tumblers) to determine if the depth of the solution had any impact to the benefits of higher CYA. Also, it wasn't practical to get that much distilled water for buckets so I kept the experiment small.

I started with my own pool water which was at FC level 7.2 ppm with a CYA of 80 ppm. All FC tests were performed using FAS/DPD. One glass had no dilution so had a FC/CYA of 7.2/80. The second glass was diluted 1:1 or FC/CYA of 3.6/40. The third glass was diluted 1:3 or FC/CYA of 1.8/20. Note that FC/CYA ratio is kept constant for all three because of the dilution method. Left in the sun for 2 hours, here are the results:

1:0 FC/CYA 7.2/80 --> FC/CYA 6.8/80 - 0.4 ppm FC Loss
1:1 FC/CYA 3.6/40 --> FC/CYA 2.6/40 - 1.0 ppm FC Loss
1:3 FC/CYA 1.8/20 --> FC/CYA 0.4/20 - 1.4 ppm FC Loss

So as in previous experiments, FC loss decreases with increasing CYA levels although with this test, the benefits seemed to be much greater. This is probably due to the depth of the water as it offers less FC protection due to lower scattering and absorption. The deeper the water, the more UV protection provided by the water so the benefits of CYA are diminished for deeper water.

This is a pretty easy test to perform so I would encourage anyone else to repeat these tests for corroboration.

This is supported by the experience of many TFP members.

This is step 1, higher CYA provides better UV protection. This is independent from the type of chlorination, the chemistry/physics doesn't give a toot about an SWG.

So why do we recommend higher CYA only for SWG-pools?

This is step 2, if you ever have to SLAM at CYA 80, then you'll likely have to drain some water and refill to reduce CYA. SLAMing at higher CYA is not much fun. The risk of an algae outbreak in a manually chlorinated pool can't be ignored, the benefit/risk ratio of running higher CYA is just not right with manually chlorinated pools. But with the regular and reliable chlorination that a SWG provides, the benefit/risk ratio is on favour of higher CYA. This is in my opinion the most important reason for the distinction between SWG and liquid chlorine recommendations on CYA levels.

And then there is step 3, why lower FC levels with an SWG? This goes down to the risk of ever falling too low in FC. I don't see a chemical reason why with an SWG a lower min FC seems to be possible. In the end it's about the cascading effects of what happens when you get close to the algae edge. Once you notice you are too low with a manually chlorinated pool, it is pretty much too late. With an SWG, you can dare to get closer to the edge before things go pear shaped. You'll likely notice that you slipped a bit lower than planned while you are still above min, rather than below.

There were attempts to explain the lower min FC levels with SWGs with permanent "superchlorination" within the cell. Maybe there is a small effect, but in reality, FC within the cell is maybe 2ppm or so above FC of the bulk water. Yes, it is slightly elevated, and maybe it does have an effect, but I would call it "superchlorination". In my opinion it gets down to risk management, as explained above.

Does it make sense to run an SWG pool at the theoretical minimum? I don't think so. You end up micromanaging the pool, having to test daily to make sure you don't slip too low, constantly adjusting the SWG-output, and you lose the main benefit of an SWG: Convenience.

Most of us that use SWGs are "running hot", a term coined by @Newdude. Pick a higher target FC, somewhere in the higher target range for liquid chlorine pools. Make sure that you create enough chlorine on hot, sunny days. And accept that your FC will shoot up a bit when it's cloudy for a couple of days in a row. Yes, your absolute chlorine losses to UV will be higher compared to running close to the minimum. But you'll lose all of that should you ever fall too low and have to SLAM - that's a real chlorine annihilator. I prefer to run a bit hot, and have a trouble free pool.

 

[mgtfp]

I guess what I meant was that chloride (CL-) is used to produce chlorine (CL2) via electrolysis. Doesn’t CL2 produce CL-?

It's a cycle. SWG turns chloride into chlorine which turns back into chloride. Repeat.

Salt (SWG) Pool
In a salt water pool you produce chlorine through the following reactions:

At the anode (positive plate):
2Cl- --> Cl2(g) + 2e-

At the cathode (negative plate):
2H2O + 2e- --> H2(g) + 2OH-

which nets out to the following where the chlorine gas dissolves in water:

2H2O + 2Cl- --> Cl2(g) + H2(g) + 2OH-
Cl2(g) + H2O --> HOCl + H+ + Cl-
H+ + OH- --> H2O
----------------------------------------------
2H2O + Cl- --> HOCl + OH- + H2(g)

or equivalently

H2O + Cl- --> OCl- + H2(g)

Using Up Of Chlorine
Breakdown of Chlorine by Sunlight (UV)
2HOCl --> O2(g) + 2H+ + 2Cl-
2OCl- --> O2(g) + 2Cl-

Net Chlorine To Breakpoint (Ammonia "Oxidation")
2NH3 + 3HOCl --> N2(g) + 3H+ + 3Cl- + 3H2O
OCl- + H+ --> HOCl

 

[mgtfp]

There is at least one state that has banned CYA.

Politicians like quick actions when a problem occurs, and move on.

There probably was an incident with unsanitary water and an outbreak of whatever disease.

Someone told the law makers that the CYA was too high, and within the allowed FC range for public pools it was not possible to keep the water sanitary.

Politician understands: "CYA is bad"
Politician decides: "Ban CYA"
Politician tells the voters how great their party is and that the opposition would never have come up with such a pragmatic solution. Move on to "fix" the next problem.

Did the politician find the best solution? No.
Does the politician give a toot about this? No.

 

[IN DEPTH]

The scientific chart often pointed to claims 50 is the sweet spot with very little gained above that. But that's in a lab with fixed UV. In the real world, Arizona and Buffalo have drastically different UV indexes and we've had thousands of data points to compare. (We'd have 360k but not every member shares their experience)

@dfwnoob pointed it out a couple weeks ago that with enough data points, we then become the science.


In a 25k gallon pool 1 gallon of 10% is 4ppm, or a reasonable peak season daily loss. If spread over 24 hours like a SWG could produce it, it would be like adding one drop every .876 seconds. Said drop would never amount to anything when UV loss was factored in. It would be burned off before it dispersed across the pool. So the higher CYA allows it to build faster than it burns off in the 60/80 range (Buffalo/Phoenix). OR. The SWG would need to be run at a higher % to overcome this, effectively shortening its life. This is the true motive as SWGs are expensive. I could probably run mine 100% with a 40 CYA and maintain target range in NY. But I'd lose 40% or more of its life.

Obviously at night the SWG is all gain. We are starting to see modern problems where people run the SWG only at night to save on electricity, and the pool is effectively a LC pool that swings normally during the day, just with a higher CYA and slightly less daily loss because of it.

Again, thousands of members have taught us this. Thousands and thousands have used it and agreed. We started where the science pointed and fine tuned it further. Science does not study us or our methods. Maybe one day.

Or a dozen other things that might stop FC production for a day or days. We reccomend daily checks and anyone who strays does so knowing that it will be on them when the SLAM has a much higher target than a LC pool.

They just don't mix. There are GREAT service people out there. If the customer is only willing to pay for once a week, said service persons hands are tied. Then there's the bad apples that every group has. Then there's the rest of them who mean well, but have been misled by the industry reps who taught them a method designed to sell overpriced products. Bioguard does not want me to have a cheap and easy pool. If they did they'd sell me baking soda as baking soda, and only when I needed it. They want to fleece me for every penny they can.

We can work with you personally. We can learn from each other at times and agree to disagree at others like civilized adults. But the industry and TFP are simply on 2 totally different paths.

As far as reconciling how a 200k commercial pool would respond to TFPC, it's simply not compatable. TFPC was never going to be for commercial applications. We are a residential based method.

TFP is politics free so I am unable to comment on legislature. I will say that neither side is happy and we can all agree with that.

You expertly danced around the question expertly and you say that you’re not into politics, .

SWCG produce relatively small amounts of chlorine gas (CL2) over a specific runtime. That same amount can be introduced using any other means (even chlorine gas itself) but have a different FC to CYA ratio recommendation. Everything else being equal…

I get the distinct impression that you’re defending a dogma with a feedback loop.

I’m not here to challenge your TFP method. I’m simply posing a simple question about the recommended FC to CYA ratio for SWCG pools versus any other chlorination method.

 

[IN DEPTH]

It's a cycle. SWG turns chloride into chlorine which turns back into chloride. Repeat.

Exactly.

Apologies for construing chloride with “salt”. I do know the difference. When speaking with homeowners, it’s easier to use common words and I tend to just keep saying it.

 

[IN DEPTH]

Politicians like quick actions when a problem occurs, and move on.

There probably was an incident with unsanitary water and an outbreak of whatever disease.

Someone told the law makers that the CYA was too high, and within the allowed FC range for public pools it was not possible to keep the water sanitary.

Politician understands: "CYA is bad"
Politician decides: "Ban CYA"
Politician tells the voters how great their party is and that the opposition would never have come up with such a pragmatic solution. Move on to "fix" the next problem.

Did the politician find the best solution? No.
Does the politician give a toot about this? No.

CT times to inactivate E.coli and crypto have been definitively proven to be extended with higher CYA concentrations. Period. No contest.

The sanitation potential of chlorine is reduced, probably by several factors including pH, but chlorinated cyanurates are weak at sanitizing. Period. No contest.

Maybe oxidation remains unaffected and the water remains quite clear, but clear water is not an indicator of sanitary water.

I think optics plays a huge role in politics where law makers must use simple, well-known terms much like did when I said “salt” instead of CL-/CL2. However, a lot of what seems to be political has strong support somewhere or less it would be found out as fraud.

 

[IN DEPTH]

Our experience here has shown, that higher CYA does provide better UV protection. If you've read through Chem Geek's chemistry sticky, you will have seen him mentioning that a number of times, but you will also have seen him admitting that he doesn't fully understand why this is the case, suggesting some ideas. Just going by the percentage of chlorine that is attached to CYA (calculated with the O'Brien model), doesn't deliver this effect. That's where those statements like "beyond 40ppm gives no additional protection" come from.

But we have seen again and again that there is an effect beyond 40ppm. mas985 for example has done extensive testing over the years to quantify this. Here his latest results:



This is supported by the experience of many TFP members.

This is step 1, higher CYA provides better UV protection. This is independent from the type of chlorination, the chemistry/physics doesn't give a toot about an SWG.

So why do we recommend higher CYA only for SWG-pools?

This is step 2, if you ever have to SLAM at CYA 80, then you'll likely have to drain some water and refill to reduce CYA. SLAMing at higher CYA is not much fun. The risk of an algae outbreak in a manually chlorinated pool can't be ignored, the benefit/risk ratio of running higher CYA is just not right with manually chlorinated pools. But with the regular and reliable chlorination that a SWG provides, the benefit/risk ratio is on favour of higher CYA. This is in my opinion the most important reason for the distinction between SWG and liquid chlorine recommendations on CYA levels.

And then there is step 3, why lower FC levels with an SWG? This goes down to the risk of ever falling too low in FC. I don't see a chemical reason why with an SWG a lower min FC seems to be possible. In the end it's about the cascading effects of what happens when you get close to the algae edge. Once you notice you are too low with a manually chlorinated pool, it is pretty much too late. With an SWG, you can dare to get closer to the edge before things go pear shaped. You'll likely notice that you slipped a bit lower than planned while you are still above min, rather than below.

There were attempts to explain the lower min FC levels with SWGs with permanent "superchlorination" within the cell. Maybe there is a small effect, but in reality, FC within the cell is maybe 2ppm or so above FC of the bulk water. Yes, it is slightly elevated, and maybe it does have an effect, but I would call it "superchlorination". In my opinion it gets down to risk management, as explained above.

Does it make sense to run an SWG pool at the theoretical minimum? I don't think so. You end up micromanaging the pool, having to test daily to make sure you don't slip too low, constantly adjusting the SWG-output, and you lose the main benefit of an SWG: Convenience.

Most of us that use SWGs are "running hot", a term coined by @Newdude. Pick a higher target FC, somewhere in the higher target range for liquid chlorine pools. Make sure that you create enough chlorine on hot, sunny days. And accept that your FC will shoot up a bit when it's cloudy for a couple of days in a row. Yes, your absolute chlorine losses to UV will be higher compared to running close to the minimum. But you'll lose all of that should you ever fall too low and have to SLAM - that's a real chlorine annihilator. I prefer to run a bit hot, and have a trouble free pool.

I can accept that the reasoning for the difference in recommended CYA concentration is due to reliability of chlorine introduction. However, that should be more transparent instead of propping up SWCGs. It’s bad reporting just like using jargon that makes understanding more difficult. If you remember taking any calculus courses, you’ll remember that is not the answer/result but how you did the math. The work is graded over the answer.

My point is that there cannot be two different FC to CYA ratios. I was just waiting for someone to say it. What I got was a bunch of people defending the TFP method to a worrisome level. Then I was censored and banned, etc etc.

Don’t hide the fact that manual dosing can be problematic! I require some sort of chemical feeder on all of my maintenance pools.

mas985 did not mention a control sample in the experiment. Experiments with only one test and one series isn't quite good enough. A collection of data points taken without a standard testing method isn’t quite good enough. This adds up to bad science even though it may be accurate.

 

[mgtfp]

CT times to inactivate E.coli and crypto have been definitively proven to be extended with higher CYA concentrations. Period. No contest

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

For example:




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:



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

 

[mgtfp]

but clear water is not an indicator of sanitary water.

True. Water being clear is not a sufficient condition for it to be sanitary. But it is a necessary condition.

 

[mgtfp]

Apologies for construing chloride with “salt”. I do know the difference. When speaking with homeowners, it’s easier to use common words and I tend to just keep saying it.

I have no problems with the term salt as a simplification when referring to chloride. I often do this myself. I just wanted to clarify your statement

and some chloride reforms with sodium to return to salt

There is no reforming with sodium, Cl- and Na+ stay separated in water, the sodium has nothing to do with the change of chlorine's oxidation state to chloride. It sounds like you are aware of this, so I apologize if that came across the wrong way.

 

[mgtfp]

I can accept that the reasoning for the difference in recommended CYA concentration is due to reliability of chlorine introduction. However, that should be more transparent instead of propping up SWCGs. It’s bad reporting just like using jargon that makes understanding more difficult. If you remember taking any calculus courses, you’ll remember that is not the answer/result but how you did the math. The work is graded over the answer.

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.

 

[newdude]

SWCG produce relatively small amounts of chlorine gas (CL2) over a specific runtime. That same amount can be introduced using any other means (even chlorine gas itself) but have a different FC to CYA ratio recommendation. Everything else being equal

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.

 

[mas985]

mas985 did not mention a control sample in the experiment. Experiments with only one test and one series isn't quite good enough. A collection of data points taken without a standard testing method isn’t quite good enough. This adds up to bad science even though it may be accurate.

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.

 

[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

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.

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

The HOCl concentration is a more accurate predictor of disinfection rate, but pool operators and regulators are generally not prepared to calculate HOCl concentration from pH, FC, and CYA concentrations. A surrogate for HOCl is to specify an upper limit to the CYA/FC ratio instead of specifying independent limits for FC and CYA when CYA is present. The model indicates that reductions in infection risk are possible by reducing the allowed CYA/FC ratio. However, the reductions in infection risk need to be balanced with the practical operation of public pools. Restricting the ratio to too low of a value will effectively eliminate the use of chlorinated isocyanurates from public pools and result in greater chlorine consumption. Furthermore, if the ratio is too low, operators may have difficulty maintaining a chlorine residual.

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

The goal of this work was to provide a sound scientific basis for recommending a limit on the concentration of CYA in public swimming pools. Meeting this objective was difficult because no guidelines for acceptable risk exist for treated recreational water. We, thus, based our recommendation for a CYA/FC ratio in swimming pools on CYA/FC ratios calculated by analyzing several risk and pool operations scenarios. The remainder of this section outlines those scenarios and describes how each was considered in the determination of a CYA/FC standard for swimming pools.
The CYA/FC ratio of 45:1 was considered a starting point because this ratio corresponds to the highest CYA and lowest FC concentrations suggested in the current version of the MAHC. However, arguments for maintaining the current MAHC 45:1 ratio are based on the absence of documented cases where this or higher ratios have resulted in a demonstrated health hazard, such as the inability to adequately control pathogen concentrations in pool water. CYA is rarely measured during an outbreak, so there are no published data to confirm or deny that CYA has been a contributing factor in outbreaks or that lower ratios would prevent future outbreaks.

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

The lowest amount of CYA needed to achieve chlorine stability was considered. Arguments for the prohibition of CYA in indoor pools and using as little CYA as possible in outdoors pools assume that it is prudent to reduce risk wherever practical. It is certainly practical to add as little CYA as needed to obtain the desired amount of chlorine stability with unstabilized sanitizers such as sodium hypochlorite or calcium hypochlorite. A CYA/FC ratio of 5–10 provides most of the stabilization with diminishing returns in additional stabilization at higher CYA/FC ratios [69]. The benefits of any incremental increase in stability should be balanced against reduced efficacy with additional CYA.

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

The results in Table 7 indicate that lowering the maximum allowed CYA/FC ratio from 45 to 20 would reduce the annual probability of Giardia infection by about a factor of two and E. coli infection by about a factor of five.

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

The risk-based model described herein supports the standard practice of swimming pool chlorination for protection of public health. The use of CYA with free chlorine in outdoor pools results in the formation of CYA-FC complexes. This provides protection of free chlorine from the effects of solar UV exposure but also alters the forms of +1-valent chlorine that are available for disinfection. Available data indicate that HOCl is the dominant disinfectant in swimming pool applications.

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

Future investigations of this topic should include information pertaining to water quality that will aid in the calculation of free chlorine speciation in water, including FC concentration, pH, temperature, and CYA/FC ratio. HOCl concentration, based on equilibrium calculations, should be reported in all such studies. Additional information is also needed regarding rates of fecal sloughing and acceptable risk of infection at public swimming pools. In addition, simulations based on more comprehensive descriptions of mixing behavior in pools, accidental fecal release, and adverse effects of high HOCl concentration may be warranted.

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

 

[IN DEPTH]

I have no problems with the term salt as a simplification when referring to chloride. I often do this myself. I just wanted to clarify your statement



There is no reforming with sodium, Cl- and Na+ stay separated in water, the sodium has nothing to do with the change of chlorine's oxidation state to chloride. It sounds like you are aware of this, so I apologize if that came across the wrong way.

I completely boogered that comment! NaCl is dissolved into water and disassociates. The Cl- is used to produce CL2 and eventually HOCL. The reduction of HOCL produces CL- among other things. CL- rejoins “hanging out” with Na.

Table salt is the most efficient and cost effective way to get Cl- in solution.