CYA Levels: Conflicting Recommendations

[AUSpool]

Hi all, I spent the last three weeks reading up and devouring as much information as I can about the care of my 14,400 gallon salt water pool, from blogs, YouTube channels, a few books, and then also going back and forth with my own Taylor test kit as well as getting readings from Leslie's pools. With the help of Leslie's I solved a pretty serious algae problem and since then I've been keeping the chemicals pretty well balanced.

There seems to be little controversy over the recommended ranges for most of my water measurements: pH, TA, CH, Free and Total Chlorine.

But what is baffling is the conflicting recommendations about CYA levels.
Orenda Tech and Pulsar Systems, which are concerned about chlorine effectiveness, seem to suggest sticking around the 20-30 ppm (maximum). Other places (Leslie's), websites, and apps (TFP PoolMath for example) seem to suggest CYA levels upwards of 50 ppm.

However, I'm concerned about chlorine effectiveness. Quick google searches on "CYA effects on disinfection" seem to suggest that you get the most bang for the buck (in terms of UV protection) at 10 ppm CYA and above that it's diminishing returns. However, at CYA levels above 20 ppm you lose a lot of chlorine effectiveness for disinfection. Bob Lowry and Orenda Tech suggest that you need chlorine levels to be at least 7.5% of CYA levels, so at 60 ppm CYA you'd already need more than 4.5 ppm free chlorine! Pulsar Systems suggests the same, except they state it by this 14:1 ratio (CYA Effects on Disinfection - Pulsar Systems)

So what am I to think? Right now it's winter and I'm keeping my CYA at 20 ppm, but given that it's hard to lower CYA levels I am scared to go higher and have algae issues down the road. All the research I've done suggested that I'm near the sweet spot, but am I sure? Heck no.

Thoughts?

Geday Chris and welcome to the forum.

One very important point to note is that the vast majority of information and/or advice within the pool industry is based on what best suits commercial applications. The industry has always found it difficult to impossible to separate commercial pools from the back yard residential pools. They find it very difficult think outside the box even just a little bit.

Over the years I’ve read through lots of articles like the Pulsar one, I stopped reading the Pulsar article when I got to “remediation of diarrheal fecal accident” part which is something that not often discussed when talking about our residential pools. My point here is really that that article is for the management of commercial pool.

The industry is quite rigid with the 1-3ppm FC limit and maintain pH at 7.4-7.6 to maximise hypochlorous acid, the active part of pool chlorine. We’ve known for ages that hypochlorous acid reacts with cyanuric acid to form chlorinated cyanurates but unfortunately the industry in general does not apply this to the benefit of residential pools. The 7.5% ratio is well known but the industry always starts from a maximum 3ppm FC and works backwards to get an ideal CYA level. It never seams to ocure to them to start from a known CYA level and apply the 7.5% to get an ideal FC level.

To that end the FC/CYA Levels is the easiest way to set FC targets.

I use the Taylor CYA comparator which starts at 30ppm so 30ppm would be my minimum but I maintain my CYA at 50ppm through winter and top it up to 70ppm through summer. We also recommend to round CYA up to the nearest 10ppm to find the ideal FC target.

 

[Lake Placid]

To piggy back on what @AUSpool stated about the commercial applications, one perspective that hasn't been mentioned but should be noted is the fact that pulsar systems rely on PH and ORP probes to sample water and adjust chemistry via electronic controllers. It’s known in the industry that CYA over 30 ppm will cause interference with the ORP probes ability to correctly read the sample stream and adjust chemistry correctly. Inherently Pulsar has a very good reason to recommend maintaining CYA at 30 or below as their systems don‘t function as reliably above this level. So I’d suggest to take their recommendations on chem levels with the knowledge that they have a need to maintain CYA levels that allow their equipment to be used within its effective operating range.

(Ok a little tinfoil hat time…..lol)

Secondarily commercial operations are reliant on legislative bodies approved regulations and health codes to get licenses to operate. Many of these regulations that were passed into law were done years ago and specifically mandate a level of FC in a “safe range“ as well as a CYA level that is considered “safe” by legislative bodies. These regs have not been updated with the data coming out of scientific studies that have taken place in the last 20 plus or so years that show a safe correlation between CYA and FC levels. Thus you’ve got a circular firing squad arrangement between “the industry” and the need to recommend levels that stay within the ranges that are already on the books legislatively. If the patchwork of regulations were changed within all the municipalities that regulate commercial pools to better reflect the updated understanding of the CYA/FC relationship would the industry begin to recommend different levels?…Perhaps so. Is there any real gain to this massive undertaking for anyone to do it…doubtful. End result, commercially we still get recommendations of FC 1-3 ppm and to not allow CYA to rise above 30 ppm………………………..because safety.

 

[ChrisA76]

Secondarily commercial operations are reliant on legislative bodies approved regulations and health codes to get licenses to operate. Many of these regulations that were passed into law were done years ago and specifically mandate a level of FC in a “safe range“ as well as …

I had heard about this in podcast with Bob Lowry too and I believe it. You’d think it would be updated based on the incredibly prevalent use of higher CYA levels. Thanks for all the info.

 

[mgtfp]

There are two factors that you also have to consider beyond the UV-protection of CYA:

1) The chlorinated cyanurates provide an HOCl reservoir.

Lets assume for simplicity that you are maintaining an FC/CYA ratio of 10%, and let's look at two, in terms of HOCl concentrations equivalent, scenarios a) and b), to maintain this ratio.

a) CYA=30ppm and FC=3ppm
Let's assume you have a pool party with a couple of kids, and a few of them are too excited to go to the bathroom. This could cost you pretty quickly something like 1ppm worth of FC.
This gets you down to FC=2ppm, resulting in a ratio FC/CYA=6.66%

b) CYA=60ppm and FC=6ppm
The same FC loss of 1ppm gets FC down to FC=5ppm, resulting in a ratio FC/CYA=8.33%

This shows that scenario b), which in the initial situation is in terms of HOCl levels equivalent to scenario a), provides a more constant FC/CVYA ratio as FC is being used. In other words, you have a bigger HOCl reservoir.


2) Higher CYA gives you a longer period of trouble free operation.

If you operate your pool at CYA=30ppm and consider CYA losses (e.g. by backwashing, rain overflow, oxidation of CYA by FC), you will pretty quickly get to a situation where the UV protection significantly decreases. And you are turning blind - below 30ppm it is difficult to get an accurate CYA reading, and at your next CYA top up you won't really know how much to add to get back to target.

Operating CYA at higher levels gives you a longer period where you don't have to worry about CYA and you don't have to micromanage the exact level.


And then let's get back to the UV-protection:

If you got through the Pool Chemistry thread that Matt sent the link to, you will have gotten to the point where Richard explained that beyond the UV protection by FC bonding to CYA there is an additional shielding effect. Neglecting this effect, you would conclude by the graph shown below the graph that Matt posted, that maintaining the same FC/CYA ratio at higher CYA results in higher absolute FC losses. But you can't ignore the shielding effect.

@mas985 has done a number of chlorine loss tests at different CYA levels over the years. This is the latest update from last year, where he optimized his method:

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

You can see from this that the additional shielding effect is quite significant, and maintaining the same FC/CYA ratio at higher CYA levels is a lot more economical. It is worth reading the original post, as it also provides a link to older measurements.


Now you have to weigh the benefits of higher CYA against the downsides. And the main downside is that a SLAM gets more challenging the higher CYA gets.

With a SWG with its constant and reliable chlorine supply, the risk of ever having to SLAM is quite low, and it is worth taking the benefits of higher CYA. The one time where a SLAM is not that unlikely is after opening after winter. But winter precipitation has by then usually reduced CYA to more SLAMable levels.

With manual chlorination using liquid chlorine, the risk of falling below min FC and having to SLAM as a consequence is higher, and therefore TFP recommends lower CYA targets compared to SWG pools. But still high enough to have a reasonable UV-protection and HOCl reservoir.

 

[ChrisA76]

The same FC loss of 1ppm gets FC down to FC=5ppm, resulting in a ratio FC/CYA=8.33%

Thank you for your thoughtful reply. I really do appreciate it.

The only part I’m not sure about in your post is what I quoted above. This assumes that at the higher CYA level it would still burn through 1 ppm of FC and not more. It could be that it takes more FC at the higher CYA level to disinfect the urine.

I’m really not trying to be antagonistic but the whole reservoir argument seems to rely on this assumption.

 

[mgtfp]

The only part I’m not sure about in your post is what I quoted above. This assumes that at the higher CYA level it would still burn through 1 ppm of FC and not more. It could be that it takes more FC at the higher CYA level to disinfect the urine.

The point is, that in both starting scenarios the HOCl concentrations are the the same, and therefore the reaction rates of HOCl with stuff are also the same, and as HOCl gets used up, the equilibrium reactions will ensure that some of the chlorinated cyanurates get released to maintain equilibrium.

Of course, once FC decreases, both situations are not equivalent anymore as pointed out in my post, and reaction rates in a) slow down faster, which is not a good thing.

I chose the urine example, because you add a fixed quantity of stuff that can get oxidized. A fixed amount of urine will "use" a fixed amount of chlorine. If there's not enough chlorine, then you'll run out before everything is oxidized, and you'll end up with high CCs.

It's a bit different with algae or bacteria that keep reproducing, where the goal is to keep killing it faster than it reproduces. A higher HOCl reservoir also helps there, but the maths is not as straight forward.

 

[AUSpool]

End result, commercially we still get recommendations of FC 1-3 ppm and to not allow CYA to rise above 30 ppm………………………..because safety.

I agree, but just to clarify here, it’s not really about safety but rather what the industry assumes as the best practice for commercial pool management in regards to pathogen disinfection rates. And a healthy dose of sales and marketing. It is never inferred that there is any safety concern in terms of toxicity with increased concentrations of cyanuric acid or indeed F/C. The CDC allows for a F/C range of 1-10ppm for residential pools and where CYA is used F/C should be maintained at a minimum of 2ppm.

I thought it interesting that this Pulsar article supplies an EPA F/C range of 1-4ppm which from their reference is from an EPA guideline for potable water supply which has little to do with either commercial or residential pool management. Pulsar have chosen a lot of figures that neatly suit their narrative. Pulsar provide commercial pool treatment solutions and seam to have a dislike for CYA which they use to promote their own products. They supply calcium hypochlorite tablets and automated feeders that use calhypo, good luck with that for any one in dry arid locations.

I really regret falling down this Pulsar rabbit hole…

 

[ChrisA76]

I really regret falling down this Pulsar rabbit hole…

Please no regrets! And I’m the one that started this Pulsar rabbit hole. Either way I appreciate your input and will likely be upping my CYA level (currently at 19 ppm) substantially as a result of this thread.

Just gotta figure out where based on the fact that it’s SWG and covered 85% of the time. But that might take some trial and error. Thank all for the thoughts and feedback!

 

[AUSpool]

Please no regrets! And I’m the one that started this Pulsar rabbit hole. Either way I appreciate your input and will likely be upping my CYA level (currently at 19 ppm) substantially as a result of this thread.

Just gotta figure out where based on the fact that it’s SWG and covered 85% of the time. But that might take some trial and error. Thank all for the thoughts and feedback!

Yeh, no real regrets, although my wife may sometimes disagree and prefer me out in yard working instead of reading through CDC, EPA, and MAHC articles.

Just record that 19ppm CYA as 20ppm, I don’t believe there’s a CYA test that’s accurate to +/-1ppm CYA.

20ppm would be still be too low for me. The Pentair QuickStart guide recommends a CYA level of 75-100ppm although thats too high for me. I round up my CYA test results to the nearest ten and then use PoolMath to dose my CYA to 70ppm.

One of the best aspects of using CYA is the greatly reduced dependency on pH as best described in this post Pool Water Chemistry

 

[mgtfp]

It could be that it takes more FC at the higher CYA level to disinfect the urine.

Just to close this one off: The main effect with urine is not disinfection (i.e. killing germs), but oxidizing nitrogen based compounds like urea, which can eat up a lot of chlorine. This is what creates the typical chlorine smell - the various levels of chloramines that occur during the oxidation process of nitrogen based stuff. You need enough chlorine to go through the complete chain of oxidation processes until in the end nitrogen gas gets released. And then you still want some chlorine left to kill the germs in the urine...

Have a look at this video: