Turnover - Necessary or not?

[sgoosman]

Turnover is a myth in pool care.
Please read this.

Interesting article but this leads to far more questions than answers. Most chemicals dissolve and disperse in water and clearly do not require a turnover. As to filtration, I've never seen a system which is capable of filtering the entire volume without at least 1 turnover. Most will require significantly more turnover. Can you request or help share the studies which are quoted in the article? I have a hard time believing "Studies have shown" when there is no citation and would really appreciate that information prior to taking that as fact. Foreign material must be physically removed and I don't understand how one reduce the counts without adequate filtration and turnover.

Regards,

Scott

 

[mknauss]

Turnover would require that you have a tank for the 'clean' water to go into while the 'dirty water' is being filtered. That does not happen in a pool. So the minute your 'clean' water returns to the pool, it is 'dirty'.

So running the pump enough each day to create your chlorine (if SWCG or tablets), skim the surface, and keep the water clean is all that is needed. The particulates in the water are drawn to the skimmer from the flow of the water.

 

[PoolGate]

Interesting article but this leads to far more questions than answers. Most chemicals dissolve and disperse in water and clearly do not require a turnover. As to filtration, I've never seen a system which is capable of filtering the entire volume without at least 1 turnover. Most will require significantly more turnover. Can you request or help share the studies which are quoted in the article? I have a hard time believing "Studies have shown" when there is no citation and would really appreciate that information prior to taking that as fact. Foreign material must be physically removed and I don't understand how one reduce the counts without adequate filtration and turnover.

Regards,

Scott

Moving particulate matter from your pool to your filter does just that; moves it. It has no bearing on water sanitation.

 

[CJadamec]

Filters trap debris and material suspended in the water. The material they trap stays there until you clean the filter. So unless you clean the filter everyday, all the material in the water stays in the water it just goes to a place where you can't see. Out of sight is out of mind.

The pumps primary purpose in a pools life is simply to circulate the water and evenly disperse the chemicals used for sanitation. On a daily basis once your water column is evenly mixed and you have stirred up the water to bring fresh chlorine to all the surfaces in the pool you no longer need to run the pump.

We have had members who were curious enough to see how long that actually takes by taking timed water tests after adding chlorine at controlled amounts. The end result of all that testing and curiosity showed that after about 30 mins the chemicals in the water were dispersed evenly from top to bottom of the pool.

This was across multiple different pools of all types and construction with both fixed and VSP pumps running at all different flow rates.

 

[HeyEng]

We have had members who were curious enough to see how long that actually takes by taking timed water tests after adding chlorine at controlled amounts. The end result of all that testing and curiosity showed that after about 30 mins the chemicals in the water were dispersed evenly from top to bottom of the pool.

This was across multiple different pools of all types and construction with both fixed and VSP pumps running at all different flow rates.

I think this is very useful information. I tend to let my pump run for an hour after adding chemicals and have seen that the chemical level will have increased to the "expected level" within that time. I also test the water on the opposite end of the pool in which I add chemicals.

 

[mas985]

I have done experiments on my own pool and found that with the pump on low speed, full chemical distribution when adding liquid chlorine occurs at about the 30 min mark.

Technically full chemical distribution is the minimum run time for any pool. Anything after that is strictly for aesthetics and/or heating purposes.

 

[sgoosman]

Everyone has some rather interesting takes on on the usage and methodology of filtration. I would argue and if desired I'll gladly write a long form details but filtration is also an integral part of sanitation. Many are correct that filtration does not "remove" pathogens (fecal coliforms, legionealla, staph,etc..) and quality components (molds and spores), the function is to sequester the contaminates from the main body of the pool. Many of these contaminates will then be unable to proliferate or have the inability to migrate from the filter. Some contaminates will proliferate, ie legionella in the filter system (particularly sand) filters. Simply put continuous sequestration of the pathogens are vital to the safety of your pool and many will grow out to exponential growth in idea conditions within 4 hrs.

As to believing one only needs contact sanitation to kill fecal coliforms, you'd be mistaken in that believe. Professionally, I've cleaned lines with chemicals and hot water 176F+ for 30 minutes and pipe flow rates of 1m/s and still found microbes alive and well in swabs and growth plates. Additionally, we all have a common belief that chlorine will immediately kill coliforms. Tables often say 19 min or so to kill. But this is an average 6 log reduction in coliforms in that time. Additionally, this does not account for killing microbes that are embedded within other organic matter which can take hours to days to kill in a chlorine rich environment. Coliforms which are sequestered in the filter could still grown out but then should be returned to the pool in a chlorine rich enviroment with high flow velocity, which is more likely to kill pathogens.

The purpose of the filter is to sequester and drop the numbers of the these safety and quality impacting organisms. Even if "clean" water is returned to "dirty" water, the overall impurity load is reduced increasing the effectiveness of the chlorine to lyse the cellular wall and kill the bacteria/organism, *unsure of the mechanism which Chlorine kills virus's) and why your filter is a crucial element in your sterilization process. Analog to pool filtration is a hepa air filter. Clean air is returned to contaminated air but always improves the air quality and will remove the air born pathogens.

This is why I'd personally want at least 1 turnover/day at minimum in my pool. Gives me the greatest chance of filtering all the water per day or 2 and catching the nasty things in a dead spot. Additionally, this prevents growth and allows your chlorine to be most effective. This is why I'd love to see the citations to ensure they tested pathogen and quality impacting organism load with 4 hrs vs 1 vs 1.5 vs 2 pool turnover per day so I can make informed judgement and decisions.

Regards,!

 

[mknauss]

This study is one of the cornerstones that lead us to dispute the turnover in pool water statement.

Take care.

 

[mas985]

First viruses and bacteria cannot be filtered out by pool filters because they are much too small. Nearly all would just pass through the filter. E-coli is only 2x0.5 microns. The best pool filters are 5 micron.

Second, even if you had a filter that would trap them, the time it takes them to make it to a filter would take far longer than it would for FC to kill it. Each turnover only passes 65% of the pool water through the filter. It would take 5 turnovers to get to over 99%.

So relying upon filter to remove pathogens is dangerous.

 

[Donldson]

Many are correct that filtration does not "remove" pathogens (fecal coliforms, legionealla, staph,etc..) and quality components (molds and spores), the function is to sequester the contaminates from the main body of the pool.

Could you please explain this sentence further? Even a DE filter can only filter down to 3 microns and the pathogens you listed are all in the sub-micron range. How can a filter sequester a pathogen when that pathogen flows right through it? HEPA filters down to 0.3 microns, there is no comparison between that and any residential pool filter.

(was typing when mas985 posted, but the question remains)

Also your comment about effectiveness of chlorine doesn't really make sense. It takes the same amount of chlorine to kill a pathogen whether it is in the bulk pool water or in the filter, and the pathogens would continue to multiply just the same whether it were stuck in a filter or in the bulk pool water. And of course this is only if the filter were trapping these pathogens, which it isn't.

Edited to add further comments.

 

[CJadamec]

Everyone has some rather interesting takes on on the usage and methodology of filtration. I would argue and if desired I'll gladly write a long form details but filtration is also an integral part of sanitation. Many are correct that filtration does not "remove" pathogens (fecal coliforms, legionealla, staph,etc..) and quality components (molds and spores), the function is to sequester the contaminates from the main body of the pool. Many of these contaminates will then be unable to proliferate or have the inability to migrate from the filter. Some contaminates will proliferate, ie legionella in the filter system (particularly sand) filters. Simply put continuous sequestration of the pathogens are vital to the safety of your pool and many will grow out to exponential growth in idea conditions within 4 hrs.

As to believing one only needs contact sanitation to kill fecal coliforms, you'd be mistaken in that believe. Professionally, I've cleaned lines with chemicals and hot water 176F+ for 30 minutes and pipe flow rates of 1m/s and still found microbes alive and well in swabs and growth plates. Additionally, we all have a common belief that chlorine will immediately kill coliforms. Tables often say 19 min or so to kill. But this is an average 6 log reduction in coliforms in that time. Additionally, this does not account for killing microbes that are embedded within other organic matter which can take hours to days to kill in a chlorine rich environment. Coliforms which are sequestered in the filter could still grown out but then should be returned to the pool in a chlorine rich enviroment with high flow velocity, which is more likely to kill pathogens.

The purpose of the filter is to sequester and drop the numbers of the these safety and quality impacting organisms. Even if "clean" water is returned to "dirty" water, the overall impurity load is reduced increasing the effectiveness of the chlorine to lyse the cellular wall and kill the bacteria/organism, *unsure of the mechanism which Chlorine kills virus's) and why your filter is a crucial element in your sterilization process. Analog to pool filtration is a hepa air filter. Clean air is returned to contaminated air but always improves the air quality and will remove the air born pathogens.

This is why I'd personally want at least 1 turnover/day at minimum in my pool. Gives me the greatest chance of filtering all the water per day or 2 and catching the nasty things in a dead spot. Additionally, this prevents growth and allows your chlorine to be most effective. This is why I'd love to see the citations to ensure they tested pathogen and quality impacting organism load with 4 hrs vs 1 vs 1.5 vs 2 pool turnover per day so I can make informed judgement and decisions.

Regards,!

So not to get overly nit picky your argument has one large hole... Or I should say one very small problem.

A coliform, virus, or even most water born pathogens are very small in size. In the case of a coliform in water we are talking 0.5 microns. In general most water born pathogens are less than 5 microns in size.

The average sand filter in a pool is only capable of catching and holding things 20 microns and larger. DE filters and cartridge filters get down to 5-10 microns in particle size. There is simply no way for a pool filter to filter out and concentrate things like ecoli.

On the other hand what was brought up was that the circulation pump distributes the chemical sanitation, in this case chlorine. I also said it circulates the water to bring fresh chlorine to all parts of the pool and circulation system. At which point the sanitation agent has enough contact time to break down the pathogens. I can't recall any mention on this site where it is said the chlorine concentrations we recommend is an instant Kil of all things bad. I can recall multiple times reading that the concentration is sufficient to kill pathogens with sufficient contact time.

It's important to keep chlorine levels through out the entire water system high enough to provide sanitation at all times to maintain a clean pool. Proper water testing and circulation are key factors to make this happen.

If anything filtration helps to remove large organic solids from the main body of water allowing there to be more free chlorine available to sanitize the water. So really in a properly maintained pool with FC levels in the right range, clean water from the pool is passed through the FILTHY filter full of heavy organic solids only to be returned to the clean main body of water.

 

[sgoosman]

Hi Donldson,

Some common misconceptions with filtration especially DE. DE creates a filter cake where the particles have nominal size of 5 to 100 micron. The diatoms have great porosity with many tiny pores as small as 0.1 micron. Please don't take my word on that:

"DE is a chalky sedimentary material, comprised of the skeletal remains of prehistoric water microorganisms (single-celled algae) [17], called diatoms. They are characterized by size in the range from under 5 to over 100 mm and porous structure with openings as small as 0.1 mm in diameter. " Citation: On the Particles Size Distributions of Diatomaceous Earth and Perlite Granulations Petrović, D.V. ‒ Mitrović, Č.B. ‒ Trišovic, N.R. ‒ Golubović, Z.Z. Dragan V. Petrović1 ‒ Časlav B. Mitrović2,* ‒ Nataša R. Trišovic2 ‒ Zorana Z. Golubović2 1 University of Belgrade, Faculty of Agriculture, Serbia 2 University of Belgrade, Faculty of Mechanical Engineering, Serbia

A few dynamic effects occur. 1) Filter cakes are formed. Even though the particle porosity is greater than the filtered particle the winding path thru will catch and sequester particles and organisms. 2) DE has many many tiny pores which catch organisms which will get sequestered, 3) build up in the filter cake will actually improve filtration and reduce particle size filtration as filter cakes grow! So a filter cake with contaminates actually perform better at filtration than a fresh cake.

Now I never said the filter would purify the water. Due to the great porosity counts will pass thru the filter. Even Reverse osmosis filters are not and cannot be used to remove bacteria although like your pool filter the filtered side will post lower counts. Pathogen counts which are bound in the filter are far less of a concern to swimmers. Also noting, wash your hands real good after cleaning your filter as there are nutrients which will accumulate in the filters which help growth. I know for fact legionella loves to grow in sand filters sadly. Neverless the filter will not remove all contaminates but help in the system.

As to bacterial life span in a pool, many might be surprised at the longevity in chlorine:


Citiation:
Factors Influencing the Effectiveness of Swimming
Pool Bactericides
G. P. FITZGERALD AND M. E. DERVARTANIAN
Water Chemistry Laboratory, University of Wisconsin, Madison, Wisconsin 53706


Indicates kill off times for a 2 log reduction in bacteria can take easily 5-10 minutes. Other citations I've seen state 19 minutes (likely test at 6 log reduction.

Anyway, my interest in this subject is now stoked, I'll be spending more free time investigating the literature looking for micro studies on pools. If your interested I'll gladly share anything interesting I find.

Regards!

Could you please explain this sentence further? Even a DE filter can only filter down to 3 microns and the pathogens you listed are all in the sub-micron range. How can a filter sequester a pathogen when that pathogen flows right through it? HEPA filters down to 0.3 microns, there is no comparison between that and any residential pool filter.

(was typing when mas985 posted, but the question remains)

Also your comment about effectiveness of chlorine doesn't really make sense. It takes the same amount of chlorine to kill a pathogen whether it is in the bulk pool water or in the filter, and the pathogens would continue to multiply just the same whether it were stuck in a filter or in the bulk pool water. And of course this is only if the filter were trapping these pathogens, which it isn't.

Edited to add further comments.

 

[JoyfulNoise]

Hi Donldson,

Some common misconceptions with filtration especially DE. DE creates a filter cake where the particles have nominal size of 5 to 100 micron. The diatoms have great porosity with many tiny pores as small as 0.1 micron. Please don't take my word on that:

"DE is a chalky sedimentary material, comprised of the skeletal remains of prehistoric water microorganisms (single-celled algae) [17], called diatoms. They are characterized by size in the range from under 5 to over 100 mm and porous structure with openings as small as 0.1 mm in diameter. " Citation: On the Particles Size Distributions of Diatomaceous Earth and Perlite Granulations Petrović, D.V. ‒ Mitrović, Č.B. ‒ Trišovic, N.R. ‒ Golubović, Z.Z. Dragan V. Petrović1 ‒ Časlav B. Mitrović2,* ‒ Nataša R. Trišovic2 ‒ Zorana Z. Golubović2 1 University of Belgrade, Faculty of Agriculture, Serbia 2 University of Belgrade, Faculty of Mechanical Engineering, Serbia

A few dynamic effects occur. 1) Filter cakes are formed. Even though the particle porosity is greater than the filtered particle the winding path thru will catch and sequester particles and organisms. 2) DE has many many tiny pores which catch organisms which will get sequestered, 3) build up in the filter cake will actually improve filtration and reduce particle size filtration as filter cakes grow! So a filter cake with contaminates actually perform better at filtration than a fresh cake.

Now I never said the filter would purify the water. Due to the great porosity counts will pass thru the filter. Even Reverse osmosis filters are not and cannot be used to remove bacteria although like your pool filter the filtered side will post lower counts. Pathogen counts which are bound in the filter are far less of a concern to swimmers. Also noting, wash your hands real good after cleaning your filter as there are nutrients which will accumulate in the filters which help growth. I know for fact legionella loves to grow in sand filters sadly. Neverless the filter will not remove all contaminates but help in the system.

As to bacterial life span in a pool, many might be surprised at the longevity in chlorine:

View attachment 97100
Citiation:
Factors Influencing the Effectiveness of Swimming
Pool Bactericides
G. P. FITZGERALD AND M. E. DERVARTANIAN
Water Chemistry Laboratory, University of Wisconsin, Madison, Wisconsin 53706


Indicates kill off times for a 2 log reduction in bacteria can take easily 5-10 minutes. Other citations I've seen state 19 minutes (likely test at 6 log reduction.

Anyway, my interest in this subject is now stoked, I'll be spending more free time investigating the literature looking for micro studies on pools. If your interested I'll gladly share anything interesting I find.

Regards!

The graph's you show are from the Fitzgerald study are well known BUT they do not paint an accurate picture of what is happening because they fail to normalize their findings to hypochlorous acid levels as opposed to the measurements they use which is total chlorine. Unfortunately the Fitzgerald study has been used by many controlling authorities as evidence that CYA should be banned from pools because it lengthens the contact time needed for chlorine to kill pathogens. However, they get the logic totally wrong - if one uses CYA in a pool, then FC levels must be raised to allow for the correct contact times. In other words, the Fitzgerald paper PROVES what the industry gets wrong all the time - that you need to have a specific ratio of FC to CYA in order to maintain sanitary pool water....the established industry standard that water can only have 1-4ppm FC, without regard to CYA, is totally wrong. As discussed HERE by Richard, when you look at the data in light of hypochlorous acid levels (which encompasses the effects of CYA buffering the chlorine), one finds that the data tracks very well with TFP's overall recommendation of maintaining a 7.5% FC/CYA ratio.

 

[Donldson]

Even Reverse osmosis filters are not and cannot be used to remove bacteria although like your pool filter the filtered side will post lower counts.

You were absolutely correct to ask for sources when a TFP article says "studies show" (and I hope we are working to update such oversights), but to hold you to the same standard I'm going to have to call [citation needed] here. Do you have anything to back up that bacteria counts are lower on the return side of a filter than the intake? Preferably a study that uses actual bacterial counts that would be found in a properly chlorinated residential pool and not water that is so contaminated as to qualify as a Superfund site. I do believe that if you put a googol of bacteria through a filter you will catch a measurable amount, but I'm a lot more dubious when it comes to real world water quality.

 

[sgoosman]

Hi JoyfulNoise,

Interesting read which clearly sparks more interest and questions. My intent was never to paint the picture on the effects or usefulness of CYA, it clearly have a very important role to play instead that although we believe bacteria die fast, which is often the case, it's not always the case. Some of the nastiest buggers are often the hardest or most persistent to kill. Building on the idea, kill times are often in minutes and not instantaneously as many people often believe which is further confounded with the requirement of contact with FC & time.

As to studies, these are inoculation studies often looking at the pathogen or surrogate pathogen of concern which are pure or coated on a host media. In the real world the situation is far far different. Fecal coliforms or cryptosporidiosis often enter bound in the host which is unfortunately fecal matter which do wonderful job protecting and delaying die off, ie longer time before death. Side not, I believe the latter pathogen is rather chlorine resistant and only effectively filtered out. It's smart for all pool owners to understand, just because pool chlorine is in a measurable level does not mean the pool is sterile and risk is involved. Which brings be back to the original point. I'm challenged in believing a 4/day run time is sufficient. Reviewing the citation which is written by an electrical engineering. The measure of necessary pool run time was based on pool turbidity, unfortunately, all because a pool looks clear does not mean it's safe. The literature is full of case studies with pools with high counts. Many of those pools had to be clear even though testing positive for coliforms. Old study discussing coliforms:

THE DISINFECTION OF SWIMMING POOL WATER
PART II. A FIELD STUDY OF THE DISINFECTION OF PUBLIC
SWIMMING POOLS
A. P. Black, Ph.D.; M. A. Keirn, M.S.; J. J. Smith, Jr., B.S.; G. M. Dykes, Jr., B.S.C.E.; and
F. E. Harlan, M.S.P.E.

The data in the study is a little vague on the FC level by demarcating at greater than 0.3PPM but the rate of testing positive for fecal coliforms is rather astonishing at 18%.

What this boils down to, is we need to find a specific study showing bacterial data vs pump run times controlled for FC. I'm going to keep looking. With that said, all filtration will have significant effect on reducing organic matter load and DE/Sand filters will contribute to removing even bacterial loads in the 1-2 log reduction ranges Few citations: http://files.dep.state.pa.us/Water/...ningModules/dw-16_de_filtratrion_wb_final.pdf , 6 log reduction in crytosporidisis W/DE Water Treatability Database | US EPA , Great sheet by the EPA showing the log reduction with different filtering techniques https://www.epa.gov/sites/production/files/documents/SWTR_Fact_Sheet.pdf.

Well interesting topic but I'm struggling to see how it's safe to run one's pump on a 4 hr recommendation!

Cheers,

Scott

 

[sgoosman]

Nothing revelatory here and additionally, I'm not recommending anything which could result in harm as my position is more filtration/cleaning and not less. As to filtration cleaning pathogen out of water and pools see my previous citations.
But to summarize, DE will give 1 (90%) to 6 (99.9999%) log reduction due to pathogen type and other factors; Cartridge filter I'd expect little effect and Sand remarkably will likely have greater performance than cartridge as it ages.

Explaining how filter cakes work, that is rather established knowledge which becon reading a Perrys Chemical Enginnering Handbook, which I won't bother cite.

As to RO systems leaking bacteria, that is known and common in industry. You are welcome to call Veolia to ask or just a quick google search will give results such as:
"Reverse osmosis can remove microorganisms. However, it is not recommended for that use (i.e., only coliform-free water should be fed to the system) because membrane deterioration can occur due to the bacteria, and contamination may occur through pinhole leaks. Typically RO treatment systems have a few components: "
Citation: Water Research Center - Reverse Osmosis

All filtration is a gaussian distribution (bell type curve) which will filter out a range of particles but sku's to some nominal average size. RO is notorious for pin hole leaks from the start where bacteria will flow thru which is exacerbated by the enrichment of the effluent phase concentrating nutrients creating a rich growth environment but this is not relevant to pool filtration.

Cheers

You were absolutely correct to ask for sources when a TFP article says "studies show" (and I hope we are working to update such oversights), but to hold you to the same standard I'm going to have to call [citation needed] here. Do you have anything to back up that bacteria counts are lower on the return side of a filter than the intake? Preferably a study that uses actual bacterial counts that would be found in a properly chlorinated residential pool and not water that is so contaminated as to qualify as a Superfund site. I do believe that if you put a googol of bacteria through a filter you will catch a measurable amount, but I'm a lot more dubious when it comes to real world water quality.

 

[mas985]

Well interesting topic but I'm struggling to see how it's safe to run one's pump on a 4 hr recommendation!

I am failing to see why it isn't just as safe as running at 1 turnover per day per your own recommendation. Why is 1 turnover a magical number?

What you are suggesting are corner cases which have been discussed several times on this forum before: Response to Cryptosporidium Post

Given the re-circulation dilution factor of 63% and assuming a filter capturing pathogens at 99%, each turnover would capture only 62% of the pathogens which means it would still be unsafe at 1 turnover (i.e. ~7 hours for your pump and pool).

In fact, to make sure that 99.99% of the water gets filtered at least once would require over 9 turnovers so by your own reasoning, shouldn't we require 9 turnovers per hour to have truly safe water? Forcing pool owners to have massive pumps and huge pumping and bankrupting power bills. That would be the only way we could ensure that those pathogens not killed by chlorine would not remain in the water long enough to harm anyone.

The infection rates from these types of pathogens are quite small in a residential pools and in most cases, you know when they occur. Add to that the ineffectiveness of using a filter to try and remove them from a re-circulation system that would take days and sometimes weeks, with a low flow rate VS pump, to fully eradicate. It is simply impractical (and very expensive) to rely upon a filter for this. Prevention is the best protection.

The FAU study followed over 100 pools for over a year and showed no indication of unsafe water. In addition, 1000s of pools from members on this forum follow these suggestions without incident. This is sufficient evidence for me.

 

[JoyfulNoise]

In a commercial/public pool, pathogenic control is incredibly important. One only has to look at German/European standards to see the lengths some will go to create sanitary water. In many of those modern designs, they use low chlorine injected right into the return stream and then, on the suction side they use a system of coagulation and filtration with a mix of UV and/or ozone to eliminate pathogens. These are pools with hundreds of people per day in them and very low levels of FC (typically under 0.5ppm). Of course, the EU does not allow for the use of cyanuric acid and so these pools need very good hydraulic design to ensure the water is properly homogenized.

However, to build off Mark’s comment, single-family residential pools really do not require the level of filtration we’ve been discussing here. The likelihood of contracting Giardia or C. Parvum is low enough to not be a big deal. If one is having a large pool party, then simply raising FC levels up should be sufficient. The kids at Preschool, Elementary school and weekly trips to Sunday school have proven to be far more efficient and debilitating disease transmission vectors than my swimming pool will ever be....

 

[sgoosman]

1. Hi Joyful,

Totally valid points and I agree COMPLETELY. Home vs commercial pools are different animals with different micro loads completely. Commercial pools are much harder to clean and maintain cleanliness. The challenge we'll find in the literature is the best and abundant work will be conducted on public pools as they infer the greatest health risk. Private pools have limited exposure and therefore limited value to study. Now many posit the greater bathing load leads to higher bacterial demand and I'd agree , but another plausible outcome is infections occur at the same as public pools rate but either go un-traced or unreported as the epidemiological evidence is insufficient or funds. Once again, I believe the incident and load is less but need to point out that is a belief and not a fact. Also agree with you, when expecting heavy load it's prudent to increase the filtration and FC.

Hi Mark, Personally I'll put little value in the FUA study. The study was conducted by an electrical engineer trying to determine how to save energy. His/their question was "Can a pool remain clear with 4 hrs of pump recirc/day". Their acceptability for pool hygiene is consumer acceptability and not pool micro safety. I know we feel a clear pool is a clean pool which is a safe pool. That may or may not be the case. Another major red flag in the study is the comment in a another study in 1981 declaring 61% study drop out rates in 1 year. In the conclusions, page 13, the study states "Of the 113 pools which stayed in the study for two summers and two winters" which implies there is a drop out rate in the study. This data is not published and is a major red flag of confirmation bias in any study. Building on this concern, the study has zero reported data and and the metrics appear to be random site visit/sampling and self reporting. Just poor, poor methodologies.

The inherit nature of water is growth without sanitation so a pool is a very un-natural albeit great pleasure for mankind but can be dangerous if not done correctly. I make pretense I know the perfect answer for cleaning. My point is our sanitation system is built on hurdle technologies"

• First line hurdle: Adequate chlorine/chemical disinfectant to kill most microbiology. This is the step which will give your 6 log reduction+
• 2nd line: Filtration (filter/pump): Removes organic load for the chlorine to be more effective and will filter out a good portion of pathogens. Well disperses first line hurdle
• 3rd line: UV/Ozone/etc... : Does more than filtration but who has it outside commercial
• 4th line hurdle: Manual intervention, removing the waste with robots or brooms, makes the chlorine more effective

So I'm not making any absurd statement like a need to run the pool to 9 turnover. That is simply trying to put absurd words in my mouth. What I'm questioning is the right amount of time to run the pump and I do not see sufficient evidence to state what is the right time. What I can say is the FAU study should probably have gone in front of an IRB which I doubt it would have passed as it is completely plausible that the study could or did cause harm to participants. I'd personally not recommend the results, as they are not convincing in answering the question: Can I run my pool pump 4 hrs/day and not cause harm to the occupants to an acceptable limit. The studies objective question is can the pool pump be run for 4 hrs/day and lead to an user acceptable clean pool which they purport to answer with weak methodology and abysmal data reporting.

Personally, I will not be following these recommendations but imagine most responsible pool owners already do not. The report suggested not running the pool pump while simmers are in the pool as it adequately mixes the pool water and will distribute the chlorine! I'll keep look for good information on the subject but in the mean time I'll take the conservative approach and recommend greater mix times and filtration. As to Richard's comments I'll have to read more into them when time permits. Very interesting but I'd probably rather have a discussion on the phone or F2f to understand the model better and involve a food microbiologist. Bacteria is a fickle thing and often surprises the smartest among us with surprising results. Lastly, I'd recommend anyone with immuno-compromised (young children, elderly, AIDS/HIV, cancer etc...) swimmers take a more conservative approach. They are more susceptible to a smaller pathogen load than the rest of us.

That is my 2 cents on the subject.

Regards,

Scott

In a commercial/public pool, pathogenic control is incredibly important. One only has to look at German/European standards to see the lengths some will go to create sanitary water. In many of those modern designs, they use low chlorine injected right into the return stream and then, on the suction side they use a system of coagulation and filtration with a mix of UV and/or ozone to eliminate pathogens. These are pools with hundreds of people per day in them and very low levels of FC (typically under 0.5ppm). Of course, the EU does not allow for the use of cyanuric acid and so these pools need very good hydraulic design to ensure the water is properly homogenized.

However, to build off Mark’s comment, single-family residential pools really do not require the level of filtration we’ve been discussing here. The likelihood of contracting Giardia or C. Parvum is low enough to not be a big deal. If one is having a large pool party, then simply raising FC levels up should be sufficient. The kids at Preschool, Elementary school and weekly trips to Sunday school have proven to be far more efficient and debilitating disease transmission vectors than my swimming pool will ever be....

 

[JoyfulNoise]

Let's be 100% clear about TFP's position - TFP never says that clear water is sanitary water..FULL STOP!

TFP has three criteria for safe water to swim in -

1. The FC/CYA ratio is properly maintained (min 7.5%)
2. CC's register less than 0.5ppm
3. Overnight chlorine loss is less than 1ppm (and typically is much lower than that)

When those three criteria exists and water clarity is such that one can see the screws holding down the deep end main drain cover (or you can call heads/tails on a coin tossed in your deep end), then and only then is the water safe and sanitary to swim in. These criteria are all over TFP and it is what everyone here who is a Guide, Expert or Mod will tell you.

At the end of the day I think you two are arguing different sides of the issue. Mark's point is that clarity and chemical homogenization are easily achieved with very little filter run time (turnovers). While FUA Study is certainly imperfect, it is the only study of it's kind as far as I have seen. Many here on TFP practice low turnover rates and we have yet to see any significant issues arise from user. Certainly the non-existence of evidence is not proof, but I have confidence that the industry standard of 2-3 turnovers per day is really not relevant to the happiness (and utility bills) of most pool owners.

Scott's point is coming from the opposite end that filtration is linked to good sanitation and there's certainly AMPLE evidence that is the case. One only has to look at water treatment facilities to know that the first line of technology in creating sanitary water is to have water enter settling tanks, for flocculation and coagulation of turbidity forming solids and for filtration and removal of these particles as they act as substrates for pathogens to inhabit and grow on. Only until after much of the water's turbidity is removed will treatment facilities proceed to chemical sterilization. One major reason for doing this is to ensure that the formation of DBPs and THMs are throughly minimized as those various chemical compounds represent a serious health hazard and hard to remove once formed. And, as is also well known, there are many pathogens that are not affected by chlorine at a rate fast enough for chemical sanitation to be effective. Protozoan oocysts (essentially eggs of single cell disease-causing eukaryotes) are completely immune to chlorine disinfection. So, other technologies such as coagulation & filtration as well as advanced oxidation processes are used to destroy the most hardy of pathogens.

In the end, the pool owner has to choose what level of safety they are comfortable with. It was not long ago that I had significant discussions with a potential pool owner who was very worried about setting up a pool for his child that was immunocompromised and susceptible to cryptosporidium. His child loved swimming but could not swim in public pools as they were simply too risky. In his case it was clear that if he wanted a personal swimming pool he's need to not only run coagulants and filtration but also would need to employ UV sanitation to make sure there was a source of disinfection that could handle any chlorine resistant pathogens. Given that those methods require a lot of turnovers, his pool filter would definitely be running well beyond what TFP recommends.

So, this is why discussions like these are so valuable as it allows us to revisit these topics and make sure we have done our due-diligence in hashing out all of the issues. I look forward to any new data that can be shared to help TFP always be better with each new swim season.

Thanks to all for the lively discussion.