Why such high CYA recommendations for saltwater pools?

[jkozlow3]

The 60-80ppm (or even 70-90ppm) CYA recommendations for saltwater pools makes absolutely zero sense to me.

My SWCG makes chlorine every single day. A CYA of 30-40 allows me to run with FC levels of 2-3 (7-8% of CYA) and have zero issues and I can adjust the SWCG output monthly to maintain these levels. This is exactly what I do.

If anything, I would expect the recommendation for high CYA to be for pools that have their pool serviced weekly (which almost everyone in my neighborhood does) where liquid chlorine is only added once a week by the pool guy.

Why would I want/need an astronomically high CYA level (and astronomically high FC levels as a result) when I'm generating chlorine all day long every day and can therefore utilize much lower CYA and FC levels. What am I missing?

 

[PoolStored]

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

The above is from the Deep End. So reader beware.

In a nutshell, a SWCG adds chlorine in small amounts over a long period. You will see that the FC/CYA Levels uses a lower % of CYA for FC when you have a SWCG. That is explained in the thread linked above. Because you use a lower FC versus the CYA level, a higher CYA level keeps the FC protected from the UV. The SWCG cannot 'keep up' during high UV periods. The higher CYA also allows your SWCG to not have to 'work as hard' to maintain the FC level in the pool during high UV periods. Higher CYA also extends the life of the cell because you don't need to produce as much FC as when your CYA is low...

 

[Pauls234]

It has to do, at least in part, with the fact that SWCGs produce a very consistent low level of FC vs using liquid where you start at the top end and it declines throughout the day until next dose, but someone will be along to explain the science behind it. (Edit - thanks Pool Stored!)

I was LC user for 10 years before last season and being a longtime TFPer I was terrified of high CYA so even with SWCG I stayed around 40 CYA. Later in the season I bumped it up to 70 to see what the fuss was all about (especially from @markayash and the results were as advertised. My daily loss notably declined due to the better UV protection. That alone will extend the cells life.

 

[jkozlow3]

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

The above is from the Deep End. So reader beware.

In a nutshell, a SWCG adds chlorine in small amounts over a long period. You will see that the FC/CYA Levels uses a lower % of CYA for FC when you have a SWCG. That is explained in the thread linked above. Because you use a lower FC versus the CYA level, a higher CYA level keeps the FC protected from the UV. The SWCG cannot 'keep up' during high UV periods. The higher CYA also allows your SWCG to not have to 'work as hard' to maintain the FC level in the pool during high UV periods. Higher CYA also extends the life of the cell because you don't need to produce as much FC as when your CYA is low...

Thanks. My SWCG has no problem keeping up. I run it @ 40% output for 6 hours per day in the peak of summer (reduced % in other months) to maintain FC levels in the 2-4ppm range at all times with a CYA between 30-40. This keep my FC:CYA ratio at the recommended 7.5% (give or take).

Just not sure why I'd want more CYA and therefore more FC. Multiple articles state that there is virtually no advantage of having CYA levels over 30 - the protective effects don't really seem to increase once you get beyond 30ppm.

 

[JoyfulNoise]

Please fill out your signature with your equipment and pool specs. That way we can use the information to better understand your pool and advise you.

Fact is, it’s your pool, every pool has unique environmental conditions, and you can do whatever you like. My guess, without knowing your equipment or how you schedule/run your SWG, is that you run your SWG harder than it needs to because you have less than the recommended CYA.

 

[PoolStored]

CYA vs UV Chlorine Loss Test Update

Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ 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...

www.troublefreepool.com

 

[JoyfulNoise]

Just not sure why I'd want more CYA and therefore more FC. Multiple articles state that there is virtually no advantage of having CYA levels over 30 - the protective effects don't really seem to increase once you get beyond 30ppm.

What articles …. Trade magazines? Other pool websites?

This is simply not the experience that has been shared on TFP. What TFP has discovered over the years is that there is indeed a very real protective effect for CYA that is over 30ppm that is not accounted for when you look at the basic chemistry of CYA, chlorine and UV light. It is for this reason that additional levels of CYA have better protective effects and why SWG’s can be run at lower output percentages.

Most industry analyses start with low CYA because they try to avoid the problems with high stabilizer levels and TFP also knows that high stabilizer levels and manual chlorination with liquid chlorine often leads to green pools. The industry also avoids higher CYA levels because they are required to state that FC can never be higher than 4ppm (without regard to CYA) which simply ignored the fundamental chemistry of CYA and chlorine.

 

[Pauls234]

I couldn't recall how closely I tracked it last year, but just checked my logs and saw this.

 

[jkozlow3]

What articles …. Trade magazines? Other pool websites?

This is simply not the experience that has been shared on TFP. What TFP has discovered over the years is that there is indeed a very real protective effect for CYA that is over 30ppm that is not accounted for when you look at the basic chemistry of CYA, chlorine and UV light. It is for this reason that additional levels of CYA have better protective effects and why SWG’s can be run at lower output percentages.

Most industry analyses start with low CYA because they try to avoid the problems with high stabilizer levels and TFP also knows that high stabilizer levels and manual chlorination with liquid chlorine often leads to green pools. The industry also avoids higher CYA levels because they are required to state that FC can never be higher than 4ppm (without regard to CYA) which simply ignored the fundamental chemistry of CYA and chlorine.

I was referring to the articles and charts like this (several variants exist online) that show drastically "diminishing returns" above ~30ppm.

This particular chart is from this article but there are many: Minimal CYA | Pillar 4

I'm not discounting real-world experiences from members here...but my SWCG has no trouble keeping up @ 40% output x 6 hours per day in the peak of Summer so that's why I was wondering why others would need to run substantially higher CYA (and therefore higher FC) levels when they are making continuous chlorine. Again, it makes more sense in my head to run high CYA and high FC when you only add chlorine once a week when the "pool guy" comes (which is 99% of people in my neighborhood it seems).

 

[JoyfulNoise]

Ah yes, the usual Orenda plots … you know that guy developed all his charts and work from TFP, right? It’s geared towards the service industry, not residential pool owners.

Those charts are generated, not measured. Meaning - they use basic equations of chlorine/UV chemistry to generate the curve. Real world data looks much more like a S-curve with a linear tail at high CYA which indicates a protective effect beyond simply the extinction of hypochlorite predicted from a simple Beer’s Law plot.

As I said, if 40% 6 hours/day works for you, that’s fine. No one says you have to change anything. But TFP can clearly demonstrate that when people with SWGs have high UV exposure, CYA above 70ppm has a huge impact on chlorine loss rates. In my own pool, if my stabilizer is below 70ppm, my SWG output has to increase by almost 50% to keep up with the daily loss. Others have very similar experiences.

 

[markayash]

2 weeks back I was starting to think my cell was failing. Was having to crank my cell
Power up more and more to maintain a FC of 5. My CYA was around 50 and I bumped it up to around 80 or 90 and with no other changes my FC went to around 13. Have since turned the power down to around 30% and it’s perfect.

Similar thing happened last year and I wrote it off as a fluke but SWG like a high CYA.
Like
Mentioned I think because yiur getting a small dose constantly it’s a good combination

 

[jkozlow3]

Ah yes, the usual Orenda plots … you know that guy developed all his charts and work from TFP, right? It’s geared towards the service industry, not residential pool owners.

Those charts are generated, not measured. Meaning - they use basic equations of chlorine/UV chemistry to generate the curve. Real world data looks much more like a S-curve with a linear tail at high CYA which indicates a protective effect beyond simply the extinction of hypochlorite predicted from a simple Beer’s Law plot.

As I said, if 40% 6 hours/day works for you, that’s fine. No one says you have to change anything. But TFP can clearly demonstrate that when people with SWGs have high UV exposure, CYA above 70ppm has a huge impact on chlorine loss rates. In my own pool, if my stabilizer is below 70ppm, my SWG output has to increase by almost 50% to keep up with the daily loss. Others have very similar experiences.

Gotcha. Thanks. That's why I was asking/scratching my head because I don't seem to have any issues with lower CYA myself (and I live in San Diego - pretty high UV).

That said, we don't use the pool a ton either.

 

[JoyfulNoise]

Gotcha. Thanks. That's why I was asking/scratching my head because I don't seem to have any issues with lower CYA myself (and I live in San Diego - pretty high UV).

That said, we don't use the pool a ton either.

If it’s not worth it to you to experiment then leave it as is because water is so expensive in CA and you can’t drain easily without incurring fines.

 

[Pauls234]

I didn't have any issues with lower CYA either, but when I bumped it up I found I could reduce my SWCG % because I was losing less to UV.

If you upped your CYA, more than likely you'll be able to further reduce your SWCG % and/or pump run time.

 

[blackout]

my SWCG has no trouble keeping up @ 40% output x 6 hours per day in the peak of Summer so that's why I was wondering why others would need to run substantially higher CYA (and therefore higher FC) levels

If you had higher CYA, you might be able to run at 30% or something (you’d have to experiment for the exact number), which is 25% less demand on your SWG, potentially extending its life by 25%.

Also, higher FC levels isn’t really relevant to production. If you run at 3 FC and start and end each day at 3 FC, it is no different than starting the day at 7 FC and starting and ending each day at 7 FC; your net is zero in both cases.

What is relevant is the amount you have to produce in those 24 hours to get at net zero. The advice (and overwhelming experience) here is that at higher CYA you’ll need to produce less FC over the 24 hours, because you’ll lose less to the sun.