Pentair cyanuric acid rec 30-50 for SWGs?

[3rdcoaster]

This is a newbie question. My SWG manual (version 3, units after Nov 2011) says

Monthly Service (Continued)

3.Cyanuric Acid:Sample the pool water and test for cyanuric acid level using a reliable test method.When using the IntelliChlor SCG the recommended ideal cyanuric acid level is 30-50 ppm.

Older version of the same manual recommends 60-80 ppm.

I understand from my initial reading here and elsewhere that cyanuric acid level influences level of free (and active) chlorine. Tested with Pentair Rainbow my cyanurate is about 40, and my chlorine is between 2-3. I noticed that with warmer weather and leaving my solar cover off, Cl level dropped a bit and I increased generator from 30% to 40%. Water is clear, so no immediate problem here, but I'm a bit confused as a very thoughtful article recommends lower range cyanuric acid (New Thinking: Chlorine/Cyanuric Acid In Balance - AQUA Magazine), as does mfg, c/w TFP pool school and many other sources, including mfg prior to 2011. Aqua mag article (and associated comments/discussion) makes point that increased cyanurate requires much higher total chlorine level to get equivalent disinfectant activity. However, lower cyanurate may require more Cl production by the SWG due to UV especially now with summer on the way.

What is the best path for me, should I increase cyanurate?
Thanks,
3rdcoaster

 

[JamesW]

The key is maintaining a fc/cya ratio of at least 7.5%.

It's usually easier and more stable at a CYA of about 60 ppm.

Pentair and most industry references don't acknowledge the fc/cya ratio. They just say 1 to 5 ppm fc.

Since they're beginning to recognize the importance of the ratio but they're not ready to recommend fc above 5 ppm, they have lowered the CYA recommendation.

At 60 ppm cya, the minimum fc is 4.5 with an upper range of about 9 ppm. With a SWG, you can usually run closer to 4.5 because the SWG constantly adds chlorine.

 

[3rdcoaster]

The key is maintaining a fc/cya ratio of at least 7.5%.

It's usually easier and more stable at a CYA of about 60 ppm.

Pentair and most industry references don't acknowledge the fc/cya ratio. They just say 1 to 5 ppm fc.

Since they're beginning to recognize the importance of the ratio but they're not ready to recommend fc above 5 ppm, they have lowered the CYA recommendation.

At 60 ppm cya, the minimum fc is 4.5 with an upper range of about 9 ppm. With a SWG, you can usually run closer to 4.5 because the SWG constantly adds chlorine.

Thanks for your reply. Is there any benefit to raising the cyanurate from 40 if stability proves not an issue? I agree, it is easy to dial up and down the (SWG% x hours running) = fc generated, and have lots more capacity since PB used the IC40 which is rated for much bigger pools. One factor--I have been using a 12mil solar cover over the fall/winter/spring, and am unsure if I will just put it away now that we are turning the corner and water is heating up into the 81-83 range with the cover on. If cover comes off during direct sun hours, UV will consume fc.

I.e., is there any other goal, or interaction with water chem factors, other than keeping the right amount of available chlorine high enough, which I now understand occurs at the fc/cya ratio of 7.5% and higher? I am amazed that professional PB never mentioned cya in my training. The cya I have seems to be left over from the puck chlorination used during first month after plaster. Cya and hardness (which seems another key factor for SW pools) are never measured as part of builder's comprehensive maintenance service. Now adding those into my monitoring....

 

[Jimrahbe]

3,

Your options are to increase your CYA or increase the output of your IC40... Increasing the output of the IC40 will just use up the total amount of chlorine it can produce faster.. CYA is cheap, a new cell is not..

Up to you...

Jim R.

 

[3rdcoaster]

thanks.

I agree, $ = PT. LOL. (and you say, cya = easy on hardware = path closest to TFP).

maybe this is a deeper dive kind of question but, I don't see an explanation why cya affects rate of fc burn by UV. I see that cya buffers fc moment-to-moment, preventing bottoming out of fc. If you start out with most of the chlorine in the pool bound to cya, when some fc burns off or kills a bug, some fc will come unbound from the cya. So it seems goal is to have sufficient buffering, not change the rate that fc gets consumed. I'm wondering I've missed something.

 

[JamesW]

Assuming a similar fc/cya ratio, the total loss per day should be similar because the amount of hypochlorite should be similar.

Higher levels of cya in the water might increase the opacity of the water to UV light, which would provide some shielding effect. However, this is not proven. It's merely speculation.

So, higher cya might reduce loss to uv. It also provides a reserve of chlorine, which helps avoid getting behind the demand.

Cya also provides a non carbonate alkalinity, which helps buffer pH change without causing pH rise.

 

[pooldv]

My pool uses less FC per day with higher FC. I've seen quite a few folks over the years who are willing to do the experiment report the same results. Same pool with CYA at 50 uses more FC per day than it does with CYA at 80. Especially for folks in very sunny places like Texas and Arizona. There are even folks without SWG who keep their CYA at 60 or more to reduce FC demand. I keep my CYA at 80 especially in July and August.

 

[Trappshack]

The cya thing is kind of confusing, I changed my pool water totally and naturally the cya was well over 100 so I added the pool conditioner and finally got it down to a 60 cya. Am I correct in saying that the only way to raise the cya is to drain a little water out of the pool and add fresh water to get to 80 cya and if I had more conditioner the cya would go down to 40. Is my thinking on that correct? Thanks

 

[Jimrahbe]

The cya thing is kind of confusing, I changed my pool water totally and naturally the cya was well over 100 so I added the pool conditioner and finally got it down to a 60 cya. Am I correct in saying that the only way to raise the cya is to drain a little water out of the pool and add fresh water to get to 80 cya and if I had more conditioner the cya would go down to 40. Is my thinking on that correct? Thanks

T,

If your CYA is 60 and you want to go to 80, all you need to do is add CYA (stabilizer)... If your CYA is 80 and you wanted to go down to 60, you would have to drain some water..

You do not want to go above 50 or so unless you have a Saltwater pool...

Thanks for posting,

Jim R.

 

[3rdcoaster]

My pool uses less FC per day with higher FC. I've seen quite a few folks over the years who are willing to do the experiment report the same results. Same pool with CYA at 50 uses more FC per day than it does with CYA at 80. Especially for folks in very sunny places like Texas and Arizona. There are even folks without SWG who keep their CYA at 60 or more to reduce FC demand. I keep my CYA at 80 especially in July and August.

Assuming a similar fc/cya ratio, the total loss per day should be similar because the amount of hypochlorite should be similar.

Higher levels of cya in the water might increase the opacity of the water to UV light, which would provide some shielding effect. However, this is not proven. It's merely speculation.

So, higher cya might reduce loss to uv. It also provides a reserve of chlorine, which helps avoid getting behind the demand.

Cya also provides a non carbonate alkalinity, which helps buffer pH change without causing pH rise.

thanks for these helpful explanations and summaries of past experience. For now, I'm going to push up SWG duty cycle and pump hours and get fc a bit higher (as measured with my pentair and poolmaster kits). Ordered a TF100, will recheck all, then seems like pushing up the cya is the way to go, ignoring Pentair recs (which I was hesitant to do). If I can get act together, maybe I can post a before and after.

Much appreciate the forum as a newcomer, thanks all.

 

[Trappshack]

T,

If your CYA is 60 and you want to go to 80, all you need to do is add CYA (stabilizer)... If your CYA is 80 and you wanted to go down to 60, you would have to drain some water..

You do not want to go above 50 or so unless you have a Saltwater pool...

Thanks for posting,

Jim R.

Thanks Jim