Lowest safe level of CYA/Chlorine

JakesPool

New member
Aug 31, 2021
3
Southern California
Just joined the TFP family after reading many threads for months. I'm just in the design phase of my new approx 50K gallon pool in sunny Southern California. The pool will be in full sun with only partial late afternoon shade. My family has a fair amount of parties and I anticipate heavy bather loads during all major holidays including lots of kids. Given the higher chances of "accidents", I need to be certain that no one will get sick while using our pool. Now before you chop off my head... I know many of you favor your tried and true method, but there has to be a reason Europe banned CYA and commercial pools limit it to

This has led to me searching for the best filtration/sanitation equipment. AFM NG? AOP? Dryden Daisy? SWG? Cal-Hypo? ChlorKing NexGen?

I'm familiar with the AutoPilot - Pool Pilot total control system that I've set up on my Grandmother's pool many years ago. I'm certainly not opposed to a Salt pool, one of my questions is Pool Pilot recommends "Pools using an ORP Controller (Oxidation Reduction Potential) such as the AutoPilot Total Control, should maintain 30-50 ppm." But I see on your TFP Chlorine/CYA chart the min CYA recommendation is 70 ppm?

I've also read an article on CYA effects on disinfection which I'm certain you can search and find. But 2 bullet points are:
  • Using this 14:1 CYA to FAC ratio, the maximum CYA concentration should be 14 ppm for a minimum chlorine concentration of 1ppm or 28 ppm for a minimum chlorine concentration of 2 ppm.
  • Considering the EPA limits of 1-4 ppm free chlorine, we recommend that CYA concentrations be kept below 14 for all chlorine levels to ensure adequate bather safety
Is it possible to maintain 14 CYA with 2 ppm FC using a SWG?

Dryden says using a product like APF removes phosphates that Algae & Bacteria need for growth thus preventing these from becoming an issue.

Why would anyone want to maintain higher levels of CYA/Chlorine? Aren't you swimming in a less safe pool? Sanitation is greatly reduced the higher the CYA levels get right?

Now before you chop off my head... I know many of you favor your tried and true method, but there has to be a reason Europe banned CYA and "While the CDC's recommended limit is 15 ppm for a commercial pool, the ideal sunlight protection is around 30 ppm... the vast majority of chlorine is already protected at 30 ppm."
Is there really a benefit to CYA over 30ppm?

Now if I can speak to filtration, has anyone used Dryden AFM NG? This glass media filters down to 1 micron & never needs replacing. My pool designer tells me that all of his commercial accounts have switched to it including some major So Cal water parks and Vegas casinos due to it's lower micron filtration and 50% less backwash water needed. Just interested in personal experience using this product.

Thanks guys for your feedback & personal experience with using any of the above mentioned products.
 

JakesPool

New member
Aug 31, 2021
3
Southern California
Another really good read from AquaMagazine "How they do it in Europe"

The big advantages of reduced chlorine levels are well known, starting with a reduction of disinfection byproducts or DBPs. DBPs cause a range of water-quality related issues including the familiar "chlorine smell," which is largely caused by trichloramines, cloudy water and other problems such as skin, eye and lung irritation.

But in order to achieve great water quality at low chlorine levels, you must reduce the amount of organic contamination present in the water prior to chemical treatment. That approach contrasts with a North American approach of using chlorine itself to oxidize organics.

"In the U.S. we have that cliché saying, 'nuke it 'til it glows' ... that's kind of the mentality when it comes to water treatment," Vore says. "It's our traditional approach where there's a basic assumption that you're using 90% of the chlorine for oxidation,
so that means only 10% is used for sanitizing. As opposed to going for low chlorine residuals and high ORP and almost immeasurably clear water, where you don't have any organics in the water and that small amount of chlorine is available for disinfection. But you've got to remove all those organics first or it doesn't work."
 

BenB

Gold Supporter
Jul 24, 2020
268
San Jose, CA
Pool Size
19500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
The observations of the article regarding "chlorine smell" etc. are nonsense and it's really hard to know where to begin untangling it.

Part of the problem is that the article compares generic "pool store" recommendations and outcomes (which we here agree suck) with random and romanticized European (not all of Europe) standards. I'm a Brit living here in the US so appreciate it when US folks give a nod to maybe the rest of the world having their stuff together for many things, but this is too vague, and besides the climates are very different to boot.

The pool industry (and the magazines / blogs are ABSOLUTELY part of that) will very happily sell you chlorine alternative systems with limited effectiveness, preying on the unscientific fear of chlorine and "chemicals". Their marketing materials look GREAT, and they can afford to make them great too with what they charge for their woo.

Nobody here has anything to sell and we have to buy practically nothing to keep our pools sparkling clean.

The FC/CYA table we use here is "modern" (by pool standards) and it results in water with far less active chlorine in the water than you do with "low FC" and low CYA. In other words, following the table and having an FC of 5-10 will actually have result in less active chlorine than FC of 1 in water with no CYA, which ironically is what the chlorine fearing folks wanted all along!

It's unfortunate we measure FC and not active HOCl directly, since that would doubtless do a lot to address the "cHloRinE bAd!!" misunderstanding.
 

cowboycasey

Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
8,648
Southern OK
Pool Size
15000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool SJ-40
You really do not want an ORP system as almost any CYA messes them up... Any kind of "other" kinds of who knows what to keep the pool clear with little to no chlorine will turn into a green pool and cost so much money it just is not worth it....

I promise we will not lop your head off, we love getting new people the information they need to keep the pool TFP clear..

Filters... For your area get a cartridge filter.. sand and DE filters take to much water to backwash and your in a drought... Get the biggest filter you can get, the Pentair clean and clear 520, clean it once a year and your good to go..

I have been running TFP since the very first drop of water filled my pool. I have had a salt water generator in it from the start.. I keep my CYA at 80 and FC at 7 at all times.. I have never had a green pool.. 2 Times I have done a SLAM as my SWG / power turned off and my water got cloudy... My friends came over and swam during the SLAM, my FC was at 31 and no one even knew I had chlorine in the pool..

In your region it would be much better to have your CYA at 80 and keep FC at 7, before you have a party take your FC to SLAM level of 30 FC or so and not worry about anything.. check after the party and of FC lower than 7 take back to SLAM level and check it the next day... You will have the clearest pool water in the neighborhood I promise :)

FC/CYA Chart

ABCs of Pool Water Chemistry
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,137
NW Ohio
The big advantages of reduced chlorine levels are well known
And this is where it all falls apart. It's a myth that low chlorine levels are better or that the symptoms you state are because of high chlorine levels. A myth that those pushing for low-chlorine alternatives are more than happy to perpetuate. This myth is what promotes the sales of phosphate removers and metallic algaecides and then because there's not enough chlorine in the water to handle the DPBs (yes, lower chlorine INCREASES DPBs!) you get all those unpleasant things that are blamed on chlorine so it also promotes the sales of non-chlorine systems. Yes, the people pushing this whole "advantages of reduced chlorine levels" are willfully promoting worse water so that they financially benefit from it.

Everything you quoted from AQUA (a magazine provided for free to industry members and financed by industry advertising) is from people who work in the industry. Their paycheck is derived from the sales of pool chemicals that aren't chlorine and are unnecessary in a TFPC pool. Now tell me their article on using less chlorine and more of the products they manufacture isn't biased and has no motives.

As for sanitation, it's really simple: the FC/CYA Chart provides a very low active chlorine content of the water (in fact, lower than the EPA limits you quote since they assume zero CYA) that has enough concentration to handle sanitation and oxidation of both bather waste and the DPBs they produce. I've been running my pool this way for over 12 years and have on several occasions been complemented on the "low chlorine system" I must be running since they don't smell it. I usually don't have the nerve to tell them it's about double what they would think is "safe" based on the marketing they've been shown their whole lives. Funny enough our swimsuits last longer too, if you want something a bit less subjective to back up the claim.

Enhanced filtration isn't the answer. Pool store cash cow chemicals aren't the answer. Learning how water chemistry works and how the various parameters in the water react with each other to create a good balance and ignoring boilerplate level recommendations is the answer.

As for the EU: well they just took the same data we did and came to a different conclusion. Ben and Richard said "CYA blunts chlorine effectiveness, so let's devise a good ratio that keeps the active chlorine level steady regardless of CYA level". The EU said "CYA blunts chlorine effectiveness. We've spent decades telling people that it's not safe to swim in higher chlorine levels and entire industries have been built around this, so backtracking and allowing higher chlorine would look bad with the voting public and be bad for business. So it would be better for our image and for the pool industry to just require less CYA."
 

JakesPool

New member
Aug 31, 2021
3
Southern California
Thanks guys for the replies. I appreciate your help in understanding my pool water chemistry.
Cartridge filters filter down to 10-20 microns and AFM NG glass filters to 1 micron. Wouldn't that be preferred?
I definitely agree SWG is the best solution. According to Taylor Technologies "The industry-recommended ideal range of CYA is 30–50 ppm". They also say there is no measurable benefit to CYA over 30ppm? At what point are you simply preserving chlorine and losing it's sanitizing power?
 
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cowboycasey

Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
8,648
Southern OK
Pool Size
15000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool SJ-40
Filtering down that low would not be preferred.. you will have to use water to backwash all the dirt out.. With a cart filter there is no backwash waiting no water except when you clean the filter once or twice a year... 8 years of real world data says that what we use hear is working GREAT... You can use the CYA recommended 30 to 50 and use up your SWG faster but we like SWG's to last longer.. With a CYA of 80 and FC at 7 is a great thing :)
 

Oly

Gold Supporter
Jun 28, 2017
2,323
Fresno, CA
Pool Size
27000
Every pool system is different and what works best for your pool requires testing and observation. If you have a quality test kit Test Kits Compared you can find out exactly what level of CYA provides the best FC protection from solar radiation and minimizes your daily FC loss, 1557413312503.png . You can then determine a proper sanitation level to keep your pool safe, FC/CYA Chart

You can also reliably diagnose algae populations in your system long before you see green, Overnight Chlorine Loss Test Use PoolMath too, this tool is gold.

Start with a quality test kit, read and understand the TFP science of balanced pool water chemistry and develop your own sanitation plan for your pool system. :cheers:
 

onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,202
Utah
JakesPool: "They also say there is no measurable benefit to CYA over 30ppm?" False.
"At what point are you simply preserving chlorine and losing it's sanitizing power?"
Answer: When there is not enough chlorine for a specific amount of CYA. The key is to make sure there is enough chlorine (and more) for a given amount of CYA. No matter how much CYA there is, enough chlorine can be added to compensate and ensure sufficient sanitation. It is incorrect to claim that a higher CYA automatically renders all chlorine ineffective.

As for stabilization, 10 ppm of CYA effectively shields and stabilizes about 1 ppm of chlorine. Meaning there is not much difference in chlorine loss when maintaining low levels of chlorine and CYA, and high levels of chlorine and CYA. Therefore, some people want to keep a good supply (or reservoir) of chlorine that will be available to handle lots of people using the pool, and by raising the chlorine and CYA levels can help provide that assurance that the chlorine will not be quickly and completely depleted.

There are various ways to properly maintain chlorine (and CYA) in a swimming pool. As such, some may prefer a low level for just chlorine, or both chlorine and CYA. And some may prefer having both chlorine and CYA higher. TFP prefers the high side for both due to benefits they believe are important. I do too.
 

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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,892
NY
Cartridge filters filter down to 10-20 microns and AFM NG glass filters to 1 micron. Wouldn't that be preferred
We are talking a max 19 microns here. Millionths of a meter or 1/24500 of an inch. I once invited a member to come see if he could spot those microns. I offered to supply the beer and promised that we would both be blackout before he found any.

At some point, it’s ‘close enough for government work’, as the saying goes. :)
 

cledee

Gold Supporter
Bronze Supporter
Jun 23, 2020
166
Concord, NH
Pool Size
18000
Surface
Vinyl
Chlorine
Liquid Chlorine
Thanks guys for the replies. I appreciate your help in understanding my pool water chemistry.
Cartridge filters filter down to 10-20 microns and AFM NG glass filters to 1 micron. Wouldn't that be preferred?
I definitely agree SWG is the best solution. According to Taylor Technologies "The industry-recommended ideal range of CYA is 30–50 ppm". They also say there is no measurable benefit to CYA over 30ppm? At what point are you simply preserving chlorine and losing it's sanitizing power?
In my own experience when I've taken CYA from 30 to 40, I noticed a big improvement in chlorine loss reduction. I don't go more than 40 because I only get about 3-4 hours max of sun directly on the pool before it gets shaded by the trees. The reason the range is 30-50 is because its a tolerable level, of being able to properly sanitize your water and save chlorine in reserve in case of increased chlorine demand and regular burn off from the sun. If you don't have a SWG pool once you get over 60ppm of CYA you are simply wasting chlorine as you will not get additional chlorine loss protection and instead you will get more chlorine stuck in reserve and you will waste more money on chlorine than you have to.
 

onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,202
Utah
If the goal is to maintain and limit the chlorine level at 3 to 4 ppm and no higher, then there is no need to have the CYA higher than about 40 ppm. There is full protection and full sanitizing. Raising the CYA any higher may result in the water not being properly sanitized.

However, if the CYA is at 60 ppm, then it is best to raise the chlorine level to at least 6 ppm. At that point, the chlorine (at 6 ppm) is receiving full protection (by the CYA at 60 ppm) from the sun, and there is enough chlorine to effectively sanitize the water.

I might add that pool water can be properly and safely maintained with chlorine and CYA levels even higher. Full protection and full sanitizing with very safe and enjoyable pool water.

There is no “ideal” or “tolerable” level for CYA or chlorine independently. They are connected to each other.

I am certain that the EPA, CDC, or Europe’s “current” limits on chlorine or CYA levels are not based on the new and understood science and what I believe to be empirical evidence. I believe changes to those limits will be forthcoming.

Jake, if you want to ensure that your pool water is always safe, I hope you decide to make sure that there is always enough chlorine in the water to handle the demands under heavy use. This is what TFP teaches.
 

Jcruiser

New member
Jul 16, 2018
3
Austin/Texas
I started out with tabs and somehow early on I read Pool School and switched to liquid chlorine. My pool is 3 years old and I have never had to "shock" my pool. I'm very DIY and learned that balance, brushing and netting organics was really the only things that mattered. I have so many creatures in my backyard both day and night that really love the vanishing edge/tanning deck to cool off, drink and bathe that it can be a game of keeping up.

My friends with pools fall into 2 categories. Either pool companies run their maintenance program or they "overthink" the problem and purchase remedies.
 
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Hal3

LifeTime Supporter
Jul 29, 2008
186
San Antonio, Texas
Pool Size
9000
Surface
Plaster
Chlorine
Liquid Chlorine
I just came back from the pool store.

Guy in front of me had an FC of 22 and complained about a green pool.

He was buying a bunch of recommended stuff.

No discussion of CYA.

I stayed out of it.
 

TexEdmond

Gold Supporter
Jun 16, 2021
516
Edmond, OK
Pool Size
25500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Guy in front of me had an FC of 22 and complained about a green pool.

He was buying a bunch of recommended stuff.
I'll bet you $100 that the printout from the pool store right at the very top said: "Maintain 1-4ppm Free Chlorine using [pool store] branded tabs"

That's what it said when my CYA was over 150 and I hadn't received my test kit yet.

50K gallon pool in sunny Southern California. The pool will be in full sun with only partial late afternoon shade.
You've entered the big-leagues. I hate to be an "all-or-nothing" type, but here goes: Be prepared for massive daily chlorine dosing, or a very large biological experiment in your yard. If you're interested in SWG you'll likely need to consult your pool builder about having two units or a commercial solution; the largest consumer ones only go up to 60k gallons. This site recommends a "safety factor" of at least 2x cell capacity to pool volume.

Is it possible to maintain 14 CYA with 2 ppm FC using a SWG?
My wet finger in the air is "heck no."

CYA's primary purpose is to protect FC from being burned off by UV radiation from the sun. Its level in the pool defines the safe minimum and maximum for swimming, and that's a sliding scale. My daily FC burn with no swimmers is 2ppm, and my CYA level is 70. I currently need about 25-30% cell capacity running the pump 24/7 to maintain steady levels. With that "cell size safety factor" I mentioned, if I ran my SWG full-out 100% with the pump 24/7, I could theoretically put 9ppm of chlorine into the pool daily. With my same 60k unit on your 50k pool, that'd only put 4.5ppm per day into your pool, and you'd be completely hosed. I wouldn't even know how to estimate FC burn due to UV in a 50k pool with 20ppm CYA, but it's roughly 1/4 the CYA. You'll definitely see more than 2ppm FC burn on a full-sun pool at 20ppm CYA.

All of this MIGHT keep your levels up enough to prevent algae, but you won't want to let any swimmers in the pool at your parties, or be prepared for large manual dosing of chlorine before, possibly during, and definitely after anyone swims.

EDIT: Don't put chlorine in the pool when people are swimming. That was a joke.
 

TexEdmond

Gold Supporter
Jun 16, 2021
516
Edmond, OK
Pool Size
25500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Dryden says using a product like APF removes phosphates that Algae & Bacteria need for growth thus preventing these from becoming an issue.
It's my understanding algae will grow in a pool with 0ppm phosphates. Here we use chlorine to keep algae from growing and to sanitize the water against bacteria and virus contamination. We generally ignore phosphates because we don't let algae grow, and know how to quickly kill it if it does. We don't use copper or silver or anything else for this purpose, because they cause other knock-on effects.
Why would anyone want to maintain higher levels of CYA/Chlorine?
Because it is economical and safe.
Aren't you swimming in a less safe pool? Sanitation is greatly reduced the higher the CYA levels get right?
If you've got way too much CYA, yes this statement is true. When I woke up to this method my CYA was above 150. There's no way I could reasonably and cheaply put enough chlorine in the pool for proper sanitization, much less if I had an algae problem.
Is there really a benefit to CYA over 30ppm?
Personal preference dicates this for a manually dosed chlorine pool. SWGs create very small amounts of chlorine over the time the pump is running, and it won't create enough to keep up with sunlight or bather load at 30ppm.
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,892
NY
Be prepared for massive daily chlorine dosing, or a very large biological experiment in your yard
+1. 50K is a truckton of gallons. 4 FC a day is 2 gallons of 10% liquid chlorine. A day. While we average 2-4 ppm loss per day across the land, your XL surface area will expose your water to more of that SoCal sun. Which is 2 huge strikes putting you well above our usual averages for daily loss. You might see 4ppm in the lesser demand parts of the season and 6ppm in the peak season.

I LOVE big pools. LOVE em !!! But be prepared that a minimum of 2 gallons a day will be needed. The side bonus of a big pool is it takes that much more to swing it. The pool will laugh at a few inches of rain being a .5% or less change in chemistry.

But. Huge But here. If the pool starts to get away from you, stopping that runaway train will be insane. So be extra vigilant while you learn to ensure you don’t go even remotely close to minimum FC. Testing is a joke, as scary as it seems at first. Literally 3 minutes in the morning and evening will keep you well on track. Once you get to know how the pool behaves, once a day testing will be fine. You’ll just know the trend that it’s been consuming 3(?) ppm a day lately and can expect it to behave similar. As the seasonal UV ramps up or down, you’ll adjust to match it.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,479
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
With regard to the Conventional Wisdom™ of that Scientific-study-that-proves-cya-is-evil® one has to actually go and dig deep to understand what that "study" is and is not showing and not just believe the conclusions. What you find in those studies (there are European studies and one that was done by the Wisconsin public health department ... who the heck swims in a pool in Wisconsin???) is that they look at the CT kill rate of chlorine on various pathogens of interest and then they vary the CYA and free chlorine (FC) concentrations to see what effect it has on the kill rates. And, low and behold, oh-my-gosh :eek::eek::eek::eek:, the kill rates get worse when you increase CYA ..... quick, drain the pool, pour gasoline on it and burn it to the ground!!!! (But wait, it's already in the ground :unsure:) ...

What all of those studies fail to do is report the CT kill rates while controlling for HYPOCHLOROUS ACID (HOCl) concentration, NOT FC. It is HOCl that is the primary disinfectant and oxidizer when you add chlorine to water. Free chlorine is a measure of HOCl, OCl- and, if CYA is present, the chlorine that is bound to the CYA. So FC in and of itself is a useless quantity to use an independent variable. When one takes their data sets and actually calculates HOCl levels and then replots the data, guess what happens?? All the CYA is eeeeevvvviiiiilllll evidence completely evaporates. Why?? Because all it takes is about 50-100ppb (that's parts per billion) of HOCl to completely sanitize water and make disease transmission very difficult. Using an FC/CYA ratio of ~ 7.5% (note - it's a ratio!) yields HOCl levels that are completely sanitizing and, because CYA is present to moderate the oxidizing power, DBP's and THM's are never really an issue.

But, sadly, all that information and hard thinking takes too much effort for people in the pool industry to care about ... they have products that they need to sell to make money so the narrative needs to remain ... can't be messing up their great profit margins with all that fancy-sciencey talk ...
 

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