CYA, Friend or Foe?

[Ezun]

I just read this article and I'm very interested in thoughts around it: Cyanuric acid: friend or foe of swimming pools?

Quote from the article:
Over the years, numerous independent and academic research has come to show that when cyanuric levels build up in the pool, ORP levels consistently drop indicating that the effectiveness of chlorine diminishes. In addition, there is a clear correlation to increased levels of cyanuric acid and the time it takes to effectively kill bacteria present in pool water. The chart below demonstrates the amount of time to kill 99 percent of bacteria at various levels of cyanuric acid and different levels of chlorine. Taking one example from the data, at cyanuric acid levels of 100 ppm, it takes 20 to 50 times the amount of time to kill 99 percent than at 0 ppm of cyanuric acid.


I'm thinking of just caping mine out at 50 and leaving it there - but most of the data around TFP (given my pool setup/type) suggests I should be closer to 70.

Trying to learn here... just want to do the right thing by the pool and by the people (my family and friends) who will be swimming in it.

Thank you for any thoughts!

 

[Richard320]

That's no secret. It's only half the story, though, probably because they're trying to sell you "patented technology for advanced oxidation pool treatment." There's a good chance that chlorine you're depending on to kill bacteria might not last long enough to do the job without CYA.

Study on this thread awhile: Pool Water Chemistry Pay special attention to the half-life graph.

 

[Donldson]

"Alternative Sanitizer" websites are quite a fun read once you really learn a lot about water chemistry. They will take some minor truth and then spin it with such fervor you wonder why their authors don't have lucrative careers working for politicians. It's impressive, just a shame it is also fearmongering sales tactic.

For good solid data read the link Richard posted above. It's a bit dated, we have learned a lot in the past 12 years, but the core concept and the chemistry are accurate.

 

[duraleigh]

They will take some minor truth and then spin it with such fervor you wonder why their authors don't have lucrative careers working for politicians.

 

[Ezun]

That's no secret. It's only half the story, though, probably because they're trying to sell you "patented technology for advanced oxidation pool treatment." There's a good chance that chlorine you're depending on to kill bacteria might not last long enough to do the job without CYA.

Study on this thread awhile: Pool Water Chemistry Pay special attention to the half-life graph.

Thanks for letting me geek out on this stuff, looking forward to digging through that thread.
Ya know what - I didn’t even look at what they were selling...Just read the article and immediately came here for the truth.

Thanks!

 

[Ezun]

"Alternative Sanitizer" websites are quite a fun read once you really learn a lot about water chemistry. They will take some minor truth and then spin it with such fervor you wonder why their authors don't have lucrative careers working for politicians. It's impressive, just a shame it is also fearmongering sales tactic.

For good solid data read the link Richard posted above. It's a bit dated, we have learned a lot in the past 12 years, but the core concept and the chemistry are accurate.

@Donldson, thanks - It’s funny to read your response (and likely very accurate), if I read an article like that by someone trying to sell alternative solutions in my industry I’d see right through it, but here I missed it. Just glad we have such open and honest people here at TFP - open to reading the article and giving it a fair shake, but pointing to evidence based information that takes the core details of what was in that article, and wraps it in more evidence and truth than spin.

.... off to geek out on pool water chemistry ?

 

[splashpad]

.... off to geek out on pool water chemistry ?

This is prob my favorite thing about TFP! The "Why's" AND "How's" are clearly explained (if you care, my SO does not, "Is the bad stuff dead? " "Yes, Hun" "Let's swim" ) and you can even start learning the "when's" & "where's" too with time!

 

[Aqua Lab Rat]

The research papers I've looked at show that most of the protective benefit of CYA is achieved with only 20-25 ppm. There's no reason to go to 70 ppm. Places like Arizona probably need a little more than Illinois, but I bet if you put in 30-40ppm that would be plenty.

 

[onBalance]

A CYA of 20-25 ppm does indeed protect around 1-2 ppm of chlorine effectively. However, when the chlorine level is at a higher level (above 4 ppm), it requires a higher CYA level to provide effective sun protection and stabilization.

Of course, when the CYA level is above 40 ppm, the chlorine level should also be raised (higher than 1-2 ppm) for adequate sanitizing efficacy.

 

[Ezun]

The research papers I've looked at show that most of the protective benefit of CYA is achieved with only 20-25 ppm. There's no reason to go to 70 ppm. Places like Arizona probably need a little more than Illinois, but I bet if you put in 30-40ppm that would be plenty.

@Aqua Lab Rat This is exactly where I'm struggling - most of the "recommended levels" show it at around 70ppm for my pool. SWCG, IG, plaster, etc. (you can see my sig)
But the papers point to what you're saying.

A CYA of 20-25 ppm does indeed protect around 1-2 ppm of chlorine effectively. However, when the chlorine level is at a higher level (above 4 ppm), it requires a higher CYA level to provide effective sun protection and stabilization.

Of course, when the CYA level is above 40 ppm, the chlorine level should also be raised (higher than 1-2 ppm) for adequate sanitizing efficacy.

@onBalance As I try to put all of this together, it sounds like CYA not only protects from the sun but it also reduces the ability for the chlorine to it's sanitizing job. Which then makes sense as to why you should be able to have a lower FC ppm at lower CYA ppm.

This is where I think both experience and the uniqueness of your own pool make a HUGE difference.

@Aqua Lab Rat & @onBalance ... here's how I'm thinking about it now.

You first need to figure out how much FC (in ppm) gets used up due to sun/sanitizing each day. But of course that's dependent on where your CYA is.
As I work through it:
1) My SWG creates 1.4lbs of chlorine in 24 hours when running at 100% capacity. This translates into 1.4*16=22.4 ounces / 4.4 ounces = 5.09ppm of chlorine that can be added to my pool in 24 hours from my SWG. (see reference below to see the full calculation)
2) keeping CYA constant (was at 50ppm during the test) and testing morning and evening, and my SWG at 50% (which means I'm generating ~2.5ppm a day), I found that I was still losing FC 1.0 - .5 ppm per day, so I bumped my SWCG to 60%
3) In my OCD-ness I was determined to get CYA up to 70ppm so increased to 70 just before making a trip (which I should have just waited on to see if running my SWCG at 60% would have worked for me.
4) I came back 3 days later to a FC of 8ppm, on a CYA of 70ppm. (I started around CF 4-4.5ppm)
5) That tells me setting my SWCG to 60% is too high given the CYA of 70ppm because I'm not losing CF as fast. So I just reduced it to 50% again and will continue to test to see if I can keep a constant FC of 5 (as determined from the FC/CYA chart: Chlorine / CYA Chart - Trouble Free Pool
6) I also like the idea of having the flexibility with my SWCG to crank it up if I have a pool party and want it running at 100% while a bunch of people are in the pool.

So basically it appears to be a function of how much you lose (sun, people, what fell in the pool overnight) and replace each day. If you're losing more than you're able to replace, then you need more CYA.

And, I think I'm comfortable at 70 CYA giving me the FC stability and keeping me at FC of 5ppm. I may play around with it over time, because I'd love to have a very low requirement of FC and therefore less exposure to chlorine for those who swim in our pool.

BUT, the FC/CYA chart says that they don't recommend going below CYA 60ppm. I'm not 100% sure why and I may dig in more someday, but the last paragraph (see below, where I've copied it for reference) leads me to believe it's through the experience of VERY savvy TFP members who have looked at both the science and the data and then took that out into the real world, which we all know behaves very differently than tests run in a lab.

Reference:
From this article: Procedure for Hyperchlorination in Public Swimming Facilities . Chlorine parts per million (ppm) is calculated by weight. One ppm is equal to 1 pound of chlorine in 1 million pounds of water. One million pounds of water is approximately 120,000 gallons. Converting to ounces, (1 pound = 16 ounces) 1 ounce of chlorine in 7,500 gallons equals 1 ppm.
If 1 ounce of chlorine in 7,500 gallons equals 1 ppm then, I need 33,000/7,500 = 4.4 ounces of chlorine to get 1ppm of FC in my pool

Last paragraph of FC/CYA Chart:
"The original Chlorine/CYA “Best Guess” chart was developed by Ben Powell. Richard Falk (chem geek) has refined and expanded on that original to produce the Chlorine/CYA Chart by Chem Geek based on experiences with members on this forum and the old Pool Forum and conformation to chemical theory."

 

[Ezun]

@Aqua Lab Rat & @onBalance
Now that I'm getting deeper into this I went back and read the TFP post here: Chlorine/CYA Chart

And reference 3 really stood out to me:
"Most saltwater chlorine generator (SWG) pools appear to prevent algae at a minimum FC level of 4.5% of the CYA level as compared with the roughly 7.5% of the CYA level shown in the "Min FC" column for manually dosed pools."

That means at 70ppm CYA, I could maintain 3.15ppm FC and still prevent algae.... so I'm thinking of continuing to target 5ppm FC, which gives me the flex of dropping by 2 ppm FC during the day without ever going below 3ppm FC.

Love this forum - where else could I have this level of discussion without funny looks?

 

[Aqua Lab Rat]

It's almost catch-22. You need more FC to sanitize at higher levels of CYA, and you need more CYA to protect a higher level of FC. You are right, you have to seek some level of balance between what you lose and what you supply. My own personal preference would be to keep a small concentration of copper algaecide to take some of the load off of my chlorine, but that's not the TPF way so I won't promote it here.