CYA for Salt Chlorinator Pools II

Hi folks....I'm new, but eager to be part of this 'wet ' wild' pool community. ;)

My present concern is about the best CYA level to maintain for a pool using an Aqua Rite Salt Chlorinator. I recently drained and refilled some of my pool in order to reduce the CYA from 100ppm to about 40ppm. I would really like to stay in this range, but for some reason the manual suggests 60-80ppm.

Does anyone else have a SWG system and what do you keep your CYA at? Why would a salt system need higher CYA?

Thanks in advance. Karin

The higher CYA helps the chlorine stick around in your pool longer. That allows you to run with a lower output setting on the SWG. I've had one for several years with cya of 70-80 and 1-2ppm chlorine with great results. I only add bleach after very heavy rains. Hope this helps, Tony

Thanks Tony....that does help. How long do you run your SWCG each day? It seems that mine is way too eager to please and my chlorine level is up at 6ppm after running the pump/filter/Kreepy thing for about 6-8 hours each day.

I know I can adjust it downward and I do....but we just had a horrifying experience with yellow algae and now I'm nervous that the alien algae will return.

I run my CYA at 35-40PPM with a FC level of 2.5 PPM. Aquarite is set on 40% and runs for 12 hours each night with pump on low speed. Water is always crystal clear.

Well for our pool my output is up a bit this year due to the hot hot summer so far here in the midwest. I'm at 50% and 8 hours per day. Water temp is 91.

Edit: forgot to mention it's more efficient to run with salt at the higher end (3400), your output is also dependent on the salt level.

The high recommended CYA level by most salt water chlorinator manufacturers seems to be a mystery to most on this forum.

I abide by Ben's "best guess" chart of CYA vs. FC and so I keep my pool at 40ppm CYA and about 5ppm FC. My Polaris AquaClear cell runs 10 hours a day as my pool is in direct sun all day.

I am interested in everyone's settings as well, since there seem to be many different lines of thinking on this:

1) Use recommended CYA 60-80 and keep chlorine level per Ben's CYA table.
2) Use recommended CYA 60-80 and ignore Ben's CYA table and rely on cell to continuously shock water plus add bleach when necessary.
3) Use lower CYA level and Ben's CYA table. Recent studies indicate the CYA can contribute to dissolving plaster and shortening it's life.
4) Use lower CYA level, ignore Ben's CYA table and rely on cell to shock water.

My current preference is #4 since I have a plaster pool and not quite at Ben's CL ppm. I am operating at a CYA of 30, 21000 gallon pool, setting 90% and run the pump 6 hours a day. I am able to maintain 2 ppm. I have calculated that with my current settings, the cell puts in about 2 ppm per day so I figure I am using up 2 ppm per day.

If anyone is interested, the aquarite/logic cell puts in 1.45 lbs/day @ 100% setting. This is equivalent to 1.45 gallons of 12.5% bleach.

I think if I upped the CYA with the current settings, the chlorine would probably rise but not as quickly as per Ben's table. I am trying to research this a bit more to see if I can predict a chlorine ppm level with different CYA levels. I would love to experment with different CYA levels but given the difficulty of reducing CYA, this is not an option.

Agree with the previous post about following Ben's guidelines. I run my CYA at about 30 ppm. I adjust the SWG so that my FC is at about 5 ppm in the morning, and it drops no lower than 3 ppm by late afternoon in full AZ sun. I run my pump on low speed 24/7, SWG at about 30% on power level 1, salt is at 2900-3000.

I've heard that using my SWCG to shock will hasten the cell's life expectancy. I don't want to hasten its demise and will probably use good ole bleach on the occasions it may need some shocking--after heavy rains.

I can only run my pump at one speed. It can adequately turn my water in a 4-6 hour period, but I leave it on for 6-8 hours....it usually starts at 8am. Should I maybe have it start later in the morning so that it runs during most of the hot afternoon part of the day and keeps adding fresh chlorine that way?

Based on your comments, I'm leaning toward a CYA of around 50---close to Ben's recommendations and also Aqua Rite's. How's that for straddlin' the fence?

Tell me more about CYA staining??? I added some the other day through the skimmer---tried to dissolve it with some warm water first, but that stuff doesn't like to dissolve, and then slowly poured it into the skimmer while it gulped it down.

I presently have some yellowish stains in corners and the risers of the steps and along the walls in the deep end that appear to be recent. Since we just had it resurfaced with some Diamond Brite in March, I'm very concerned.

We had a bout of yellow algae about a week ago---which I think is gone. (Cleaned the filter daily.)
We did a partial water change to lower the CYA only to find out that the city water was full of phospates....plus I forgot to add a sequestering agent till after it had been filled. Then after going to 4 pool stores and getting 4 different CYA readings of : 15, 25, 30 and 60 all from the same sample, I added some CYA to bring it up to 40. Yes....I do need a life...

So now I'm wondering what the culprit is for the stains:

From the Yellow algae?
From the new water full of phosphates etc?
From the additional CYA?

Other than for the stains, the pool and water look great: clear and blue....sigh..I should be in there right now instead of typing about it....
FC 6.5
TC 6.5
PH 7.4
Hardness 200ppm
Alkalinity 100
CYA 40
Salt 3100

I've never heard of CYA staining - it could be due to metals or algae

Karin & Others,

The 60 - 80 ppm CYA recommended by the SWCG manufacturers is because the cell instantaneously creates a high concentration of chlorine, and kills the chloramines as well.

Without the high CYA, the chlorine would be used up rapidly before it gets into the body of the pool.

With my SWCG, a 50 - 60 ppm CYA level appears to work fine. So 50 ppm you are using is in the ballpark.

Regarding the staining, it could well come from your fill water, but others with more experience can help you. Have you tried to brush this stain? To my knowledge CYA does not stain, otherwise we would be using something else.

Your water chemistry apart from the CYA is also in the ballpark, and I can well understand your frustration with 4 pool stores giving you different readings, so I take them with a pinch of salt (pun intended);) They do not know how to be consistent. Once you do it yourself the same identical way each time, you will be less frustrated:D

mas985, I would use option #2, based on what I said at the beginning. The cell should produce the chlorine regardless, and if not you can always aise the output. A bit of trial & error. I have not heard of CYA dissolving plaster pools. That's a new one to me. Will have to investigate.

Hope this helps.

Pat

Well, I went to the horse's mouth and called up Aqua Rite to ask them about their higher recommended CYA levels. After 10 minutes of listening to some vintage elevator music, the rep told me that the chlorine that a SWCG makes is different than the regular chlorine you just add to a pool.

That's why they want a higher CYA---to protect it from sunburn.

Was she just trying to get me to hang up, or does that sound plausible? Hmmm...

I think you'll have to experiment a bit on your CYA levels. I keep mine within the recommended range due to full sun exposure. I think most pools would be fine with 50ppm and after all, stabilizer isn't cheap.

Quote:

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Originally Posted by Karin

Well, I went to the horse's mouth and called up Aqua Rite to ask them about their higher recommended CYA levels. After 10 minutes of listening to some vintage elevator music, the rep told me that the chlorine that a SWCG makes is different than the regular chlorine you just add to a pool.

That's why they want a higher CYA---to protect it from sunburn.

Was she just trying to get me to hang up, or does that sound plausible? Hmmm...

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She told you the same thing that PatL34 stated above and the same thing that I have stated in other threads. There is a difference between manually chlorinating and producing chlorine by electrolysis. I have spoken to tech support at Goldline Controls, Poolsean, who is in this forum and works for AutoPilot Systems (Pool Pilot SWG's), and some of the dealer literature that I have access to from my job (the store I work at sell several brands of SWGs) all are saying the same thing. It is better to run the CYA level higher in a pool with a SWG. I run mine at 70 ppm with my Aqualogic PS-8 (Goldline Controls). I also test a lot of water all day and can access histories of test results. About half our customers have SWG's installed and there are several that have been running CYA at 30-50 ppm. I have notices that these people have not been able to maintain adequite FC levels, run their cells at very high outputs, and some have had problems with algae blooms, including Mustard Algae. I have not seen any of these problems in the ones running higher CYA levels and keeping the FC at about 3 ppm or slightly higher. It is a small sample, maybe about 50 or 60 customers but the trend I have seen is unmistakable!

Here is the CYA article about plaster and CYA:

http://findarticles.com/p/articles/m...4/ai_n15932555

Although this probably applys more to very high CYA, this was why I was reluctant to go to higher CYA levels. I may end up going a bit higher anyway.

Quote:

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Originally Posted by mas985

Here is the CYA article about plaster and CYA:

http://findarticles.com/p/articles/m...4/ai_n15932555

Although this probably applys more to very high CYA, this was why I was reluctant to go to higher CYA levels. I may end up going a bit higher anyway.

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The sudy was done by ARCH chemicals! These are the same people who put copper into trichlor pucks. I am sure they are talking about CYA levels well above 100 ppm! There is also evidence that sulfates from using dry acid can affect the plaster so there can be multiple causes for damage to the plaster finish. The article did state that ARCH chemical recommeded switching between trichlor and other forms of chlorine to keep stabilzier levels from going too high. Does this mean that they are starting to read the Pool Forum? Seem like THAT piece of advice has been given on here for a very long time!:D

Looks like the SWG manufacturers understand their products better than we do. It's in their best interest to suggest CYA/CL levels that will work in a vast majority of pools, otherwise people would be cursing them instead of singing their praises. Partially based on advice in this forum, my CYA was around 40 last year and I kept having to crank up the output. Raised it to 60 this year and now run at 40-50% instead of 60-70%. FC levels are more stable and acid use is down also, maybe since it's working less and maybe since the plaster is now 2 yrs old.

If your cell output is down your pH should not drift up as quickly since you are manufacturing less sodium hydroxide! Another reason to run the cya a little higher! Actually, your results are pretty typical of the things I have seen with my customers when viewing their histories. The vase majority of them bring water in for testing weekly or bi weekly and the LaMotte software we use allows me to graph test results which makes spotting these trends easy to see. (Now you all know what I do when I get bored at work!) ;)

Great thread - thanks to everyone posting.

For what it's worth - I'm on my first year with a Pool Pilot, and *have* been able to keep FC in the pool even with CYA in the 30 range (28K gallon pool, 48 size cell, power level 2, 20% to 33% usage). I have been debating about where to keep my CYA levels, too. I have kept my new solar cover on at all times this year except for when we actually are using the pool. One theory is that my blue/silver solar cover has helped me maintain a higher FC level in the pool, since there is less sunlight hitting the water. I chose blue/silver because I wanted to preserve heat from my heat pump.

However, thanks to all these discussions, and the fact that we are now in full summer "school is out" mode - meaning more time with the cover off and a higher bather load) I bought 2 bottles of hth brand CYA at my local hardware store to raise the level to around 50-60. Interestingly, the hth bottle is starting to warn people of CYA levels -- it says 20-40 is ideal, and it also says that chlorine effectiveness is severely limited over 100.

One other boast - I used plenty of borax to stabilize my ph last year, and added more this spring. My ph has been constant at 7.2 all year! My theory - lots and lots of acidic rain in the Northeast this year. So I expect the ph to eventually drift up -- although we have rain in the forecast for each of the next 7 days...

Related boast - between the rain and the solar cover, I have not added one drop of water to the pool - on the contrary, I have had to drain inches off several times!

Final boast - 2nd year of bbb, perfect water every day this year - nothing added to pool except bleach (pre-SWG), polyquat (early spring, to make sure no algae before the cover came off), baking soda (to bring my alk up in early spring), and borax (pre-SWG, to bring ph up to 7.4, though it never moved)

last reading:
FC 3
CC 0
CYA 30 (will raise to around 60 for SWG, but no worries)
TA 90 (may raise with some baking soda, but no worries)
ph 7.2
salt 4400 ppm (overcalculated when I added it for the SWG; no worries)
calcium - doesn't matter - vinyl pool with titanium core heater

:)

Ok, I think I am convinced. I will try a CYA level closer to 60 ppm. It will be interesting to see how much the CL level rises with a CYA rise.

Last week I raised my CYA from 30 to about 55. After a week of running with the higher CYA, I have come to the conclusion that it had no affect on my residual chlorine level. During this week I did not change my pump run time or the chlorinator setting. Also, pool temp and PH where about the same.

CL = 2 ppm @ CYA 30 ppm
CL = 2 ppm @ CYA 55 ppm

So the graphs from the CYA study are correct in that chlorine retention does not increase significantly for CYA levels more than 25 ppm even for a SWG pool.

One other question. Assuming the same residual, is a SWG any different than an ORP controller with liquid chlorine? Both would need to add chlorine to the pool at the same rate for the same residual. To me at least, once you get past the chlorine injection method, there is no difference. Therefore, why should the CYA levels be any different? Also, the argument about shocking in the cell for SWGs also applies to the liquid chlorine. The chlorine concentrations would be just as high near the injection point.

Sorry for keeping the debate going but there seems to be a lot of conflicting information, theories and experimental results.

Quote:

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Originally Posted by mas985

Last week I raised my CYA from 30 to about 55. After a week of running with the higher CYA, I have come to the conclusion that it had no affect on my residual chlorine level. During this week I did not change my pump run time or the chlorinator setting. Also, pool temp and PH where about the same.

CL = 2 ppm @ CYA 30 ppm
CL = 2 ppm @ CYA 55 ppm

So the graphs from the CYA study are correct in that chlorine retention does not increase significantly for CYA levels more than 25 ppm even for a SWG pool.
but you are still not within the recommend range of 60-80 ppm. Try raising it up to 70 ppm and see what happens. I find that I lose chlorine quickly when my CYA is below 60 ppm and even 60 is iffy.
One other question. Assuming the same residual, is a SWG any different than an ORP controller with liquid chlorine? Both would need to add chlorine to the pool at the same rate for the same residual. To me at least, once you get past the chlorine injection method, there is no difference. Therefore, why should the CYA levels be any different?
Because the FC levels in the cell when the cell is generating are VERY high. It is not just shock level...more like 'supershock' level. The level is much higher than can be achieved by manual chlorination!
Also, the argument about shocking in the cell for SWGs also applies to the liquid chlorine. The chlorine concentrations would be just as high near the injection point.
No, it would be MUCH higher with a SWG which is generating chlorine gas which then dissovles in the water to form hypochorous acid. If you had an automated chorine gas injection system that was introducing the gas into a very small chamber of water (the size of a generator cell) it might be similar but a dosing pump with liquid chlorine will not reach the same concentrations nor will it come close.

Sorry for keeping the debate going but there seems to be a lot of conflicting information, theories and experimental results.

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Hope this helps.

Hi all, esp Karin who started this :) (I'm going to TRY not to rant) Karin, the tech did lie to you, chlorine is chlorine is chlorine - Pat and Evan might be on to something with the introduction method, but the chlorine is the same (and made the same way most chlorine sold is made, be it a gas, puck, liquid or granual).
My problem has always been with the reason for a higher cya for salt pools, the reason proffered by Pat and Evan is about as intellectually satisfying as a ricecake satisfies a dieter. They understand chemistry a LOT better than I, but it sounds like they're quoting chapter and verse from the SWG makers. I started a rant down in the "China Shop" about this (and something else), yet none of this was brought up. So what if you are super, super shocking the water as it passes through an energized cell? Killing combined chlorine is one of the things we all do when we add bleach (chlorine) to the pool, it just does a better job of it. If it takes the entire production of cl to counteract the cc, the unit isn't dialed up enough (though I doubt that cc takes all the cl that's being produced). If it's the uv that is stealing the cl, cya will help that, but at the same time, the kill time for ... yuckies is reduced, people who follow Ben's Best Guess won't be able to generate enough to satisfy it's requirements - if you're saying that BBG doesn't apply to SWG's then SAY SO, Ben is an intelligent person and if you have data that contradicts his 'best guess', he'll probably welcome it and ammend the BBG to reflect that. I, until I hear otherwise, will follow the Best Guess and keep my pool owners @ 30 -40 cya, because they won't (or can't) understand that violating all the literature they've recieved and instructions they've been given, will be a good thing (they are pool store zombies and cl > 3 ppm = BAD). Are you sure that the SWG manufacturers aren't just trying to get people to generate more cl - they'd sell a lot more replacement cells if every one they sold had a longer run time? I hope I haven't ranted here, just a few points that came to mind as I read and reread this topic.
mas985, thanks for the link, now I know that Arch is within 1/2 hr from me, I'll gladly accept donations for an assault rifle and ammo, and a defense fund to protect me when I go down there and 'set them straight' ;)

waste,

Doesn't it make sense to try the 60 to 80 CYA range and see how it works with a SWG? If the manufacturers, etc. have determined that the super chlorination of the water as it passes through the cell helps reduce the need for active chlorine (not tied up by CYA) in the pool than why not give it a whirl? The important thing is to keep algae and other nasties at bay so if people are running their SWGs sucessfully in the 60-80 range and not reporting any problems than there must be something to it.

If we run with a CYA under 60 than the cell would need to work harder to sustain a given residual chlorine level, which should shorten the cell life. So it's not a matter of the manufacurers trying to sell us more replacement cells.

I just installed a SWG so I'll see how it goes while follwing the manuf. suggestions. Otherwise, I might be shortening the cell life unnecessarily.

Quote:

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Originally Posted by waste

Hi all, esp Karin who started this :) (I'm going to TRY not to rant) Karin, the tech did lie to you

I have to disagree with this!

, chlorine is chlorine is chlorine - Pat and Evan might be on to something with the introduction method, but the chlorine is the same (and made the same way most chlorine sold is made, be it a gas, puck, liquid or granual).
My problem has always been with the reason for a higher cya for salt pools, the reason proffered by Pat and Evan is about as intellectually satisfying as a ricecake satisfies a dieter. They understand chemistry a LOT better than I, but it sounds like they're quoting chapter and verse from the SWG makers. I started a rant down in the "China Shop" about this (and something else), yet none of this was brought up. So what if you are super, super shocking the water as it passes through an energized cell? Killing combined chlorine is one of the things we all do when we add bleach (chlorine) to the pool, it just does a better job of it. If it takes the entire production of cl to counteract the cc, the unit isn't dialed up enough (though I doubt that cc takes all the cl that's being produced). If it's the uv that is stealing the cl, cya will help that, but at the same time, the kill time for ... yuckies is reduced, people who follow Ben's Best Guess won't be able to generate enough to satisfy it's requirements - if you're saying that BBG doesn't apply to SWG's then SAY SO, Ben is an intelligent person and if you have data that contradicts his 'best guess', he'll probably welcome it and ammend the BBG to reflect that. I, until I hear otherwise, will follow the Best Guess and keep my pool owners @ 30 -40 cya, because they won't (or can't) understand that violating all the literature they've recieved and instructions they've been given, will be a good thing (they are pool store zombies and cl > 3 ppm = BAD). Are you sure that the SWG manufacturers aren't just trying to get people to generate more cl - they'd sell a lot more replacement cells if every one they sold had a longer run time?

Here is where your rant falls apart. I test a lot of water and I can tell you that raising the CYA into the 60-80 ppm range allows you to turn the output DOWN on the cell...not up! I have oberved with my own system that when the CYA drops to about 50 ppm I have to almost double my run percentage!

I hope I haven't ranted here, just a few points that came to mind as I read and reread this topic.
mas985, thanks for the link, now I know that Arch is within 1/2 hr from me, I'll gladly accept donations for an assault rifle and ammo, and a defense fund to protect me when I go down there and 'set them straight' ;)

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I guess we're headed for the china shop again!:eek:;)

I hear you waste :)

I also trust the chem experts here but I really would love to see more evidence. The SWG manufacturers must have that evidence to support their recommendations right? Where is it?

I use a SWG and currently have my CYA at 40. The SWG is on its lowest setting and is maintaining Free chlorine very well, maybe it could do better but I've been watching this thread before I add more CYA.

I figure if my pool is sparkling and my SWG isnt dying I'm ok. I can always add later if I become convinced that a high CYA is really superior.

After thinking about this a bit more, I wondered what the actual chlorine ppm would be leaving the cell given the production rate of the cell. To find out, I started with the maximum production level of my Aqualogic cell which is 1.45 lbs/day of chlorine (assumes 100% setting running 24 hours/day). Thus the production rate in GPM would be;

1.45 lbs/day * .125 gallons/lbs * 1 day / 24 hrs * 1 hr / 60 min = 1.26e-4 GPM

For my pool, the water flows at about 90 GPM (estimated from pump head curve, psi and suction in. mg.) so the maximum ppm leaving the cell would be 1.26e-4/90 or 1.4 ppm continuously. This is of course is added to the existing ppm but still it is not exactly shock level.

So if it is true that the cell does indeed have a very high level of chlorine in the cell, then the cell must either produce chlorine that is very unstable and reverts back to salt shortly after production and/or, very little of the water going through the cell is actually between the plates of the cell (ie. reduce volume of water, increased CL ppm).

Looking at the interior of my cell, I noticed that the plates only take up about half of the area of the cell which means about half or a bit more of the water never touches the cells but goes around them. Still this would only double or triple the ppm level in the cell.

So the only plausible explanation for a very high chlorine levels in the cell is that the chlorine gas is very unstable, which I think someone has already pointed out. It would seem that most of the chlorine reverts back to salt before or shortly after exiting the cell.

Therefore, the only explanation I can gather for the need of high CYA, is that during this temporary phase of high chlorine, the high CYA may prevent some of this unstable chlorine from reverting back to salt. So the CYA may have two jobs, one for UV and another for stabilizing the chlorine in the cell.

Also, from what I understand, chlorine has two jobs. First is for sanitation which kills all of the nasty bugs in pool water. From what I have read, this does not require a very high residual to accomplish so even 60-80 ppm CYA can usually accomplish this fairly quickly or quick enough.

The second job of chlorine is oxidation which removes all of the other stuff such as sweat, suntan oil and algae which is a big one. Higher levels of chlorine are required to accomplish this. However, it is not necessary to remove this stuff in seconds or minutes but is sufficient to remove in hours or even days.

So it would seem that the high CL in the cell does much of the oxidation, which can be accomplished over hours or day, and the CL residual is responsible for killing the bugs, which can be accomplished with a low CL and a fairly high CYA.

The only anomaly to this whole theory is that my residual chlorine did not increase with an increase in CYA which I would have expected. I am willing to bump it up to 70 just to make sure there is not something else going on.

Sorry for the long thought experiment but I would like to fully understand the SWG process and as Waste has pointed out, so far, we have not seen a comprehensive explanation. This is my first attempt at one but I am sure it has some flaws.

I run my CYA at 35-40 PPM with 2.5 PPM free chlorine. Pump is set on low speed for a run time of 12 hours each night with Aquarite set at 40%. The system manages to maintain levels even after the heaviest rains. Pool has been crystal clear since startup. Just got a free pool fill up yesterday with 3 inches. Nice to see some rain during the summer in south Texas.

Quote:

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Originally Posted by mas985

After thinking about this a bit more, I wondered what the actual chlorine ppm would be leaving the cell given the production rate of the cell.

(Deleted long duplicative quote -- use links if needed Waterbear; don't requote the W...H...O...L...E L...O...N...G thing! PoolDoc)

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If your hypotheses about the oxidation is correct then monitoring the CC at lower CYA and then again at higher CYA would be a telling factor!

I started commenting on appropriate CYA levels in an SWG pool in the CYA / Pool Pilot Question thread and I was pointed to this thread which has been very informative (and has me eat crow).

Obviously with my technical interest I would like to get to the bottom of why higher CYA levels are needed in an SWG pool. Assuming the data on the breakdown of free unbound chlorine vs. chlorine tied up in CYA is correct, then the amount of extra work (time) the SWG needs to be on at 40 ppm CYA is only 12% higher than at 80 ppm CYA with 3 ppm FC (it's a 45% increase in work or time going from 80 to 20 ppm CYA). Since most people see a much bigger jump than that (to maintain the same FC level), either the chlorine breakdown data from sunlight is wrong or CYA is needed in the SWG process to improve its efficiency.

It may very well be that what was said earlier on this thread is what is happening. Namely, that rather high localized concentrations of chlorine (HOCl, OCl- from dissolved Cl2) are generated and that with CYA these high concentrations get tied up quickly before they have a chance to breakdown. I find this somewhat surprising as a decent flow rate should dilute the concentrations rather quickly, but physical flow rates are usually not nearly as fast as most chemical processes (more on that later in this post).

The best way to test this theory would be with a pool that is covered to minimize the breakdown from sunlight to remove that factor from the experiment (also try not to use the pool during the experiment). Since the chlorine demand would be lowered, the chlorine generator cell should be set to run less frequently (lower percentage) to maintain a constant FC level, but the cell should be run at the normal power level used in a typical uncovered pool. Start out with a CYA level of 40 ppm or below -- way below, such as 20 ppm, would be even better. Record what percentage of time the cell needs to be on to maintain a constant FC level (say, 3 ppm). Then add CYA to the recommended range of 80 ppm. Adjust and record the percentage of time the cell needs to be on to maintain a constant FC level. Report back to this thread your results.

The above experiment was sort of done by some members of this forum (and posters to this thread) but I don't believe a cover was used so the variability in sunlight is a problem since this is a huge factor in chlorine breakdown.

I am still puzzled by the prevention of algae in an 80 ppm CYA 3 ppm chlorine pool since that only produces 0.015 ppm HOCl at a pH of 7.5 which is enough for disinfection, but presumably not enough for preventing algae (in Ben's experience). Though some have said that the higher chlorine concentrations in the SWG cell may kill algae, that would not be true for any algae that adhered to the plaster. So maybe the SWG cell kills free-floating algae and that usually that is good enough.

A post from "chem geek" would be incomplete without some technical analysis to scare the bejesus out of 90% of the forum, so stop reading at this point if you're (rightfully) frightened by chemistry.

I actually have the rate constants for the conversion of HOCl into the chlorinated cyanurates (i.e. the take-up by CYA). My rough calculations show two things. First, that a level of CYA of around 50 ppm may be the concentration where the rate of take-up by CYA of incrementally generated chlorine in the cell is equal to the generation rate of this chlorine. This lends support to the theory that the CYA helps the chlorine generation by preventing the buildup of unbound chlorine (i.e. HOCl and OCl-). Second, the incremental concentration generated by the cell is rather small so this build-up theory only works if there is a very high local concentration at the generation site (the electric plate) and that is certainly plausible. However, this whole business about superchlorination is a bit overblown since the calculations show that it would take nearly 100 turnovers of the pool water to shock it with the equivalent of 10 ppm. On the other hand, a shock of 1 ppm takes only 10 turnovers and 0.1 ppm only one. Therefore I don't believe the theory of the "supershock" is the appropriate one because not enough water is exposed to 10 ppm or higher levels of chlorine, but free-floating algae even with Ben's chart is prevented by 0.05 ppm HOCl.

Richard

Richard,

I can tell you from personal experience, I was the R & D director for AutoPilot at one time, that the concentration of chlorine within the cell is WAY in excess of 10 ppm. It was more along the line of 80 ppm, as determined by MANY dilutions of the water sample directly from BETWEEN the electrodes.

Remember, chlorine gas is produces with quickly gets absorbed by the water yielding a purer sodium hypochlorite. This certainly is sufficient to treat the water at a shock dose, regardless of the flow rate through the cell. However, we've found that by slowing down the water flow, you allow more "contact time" to process the water and rid the combined chlorines, and kill the "bad stuff". Basically, it increases the efficiency of the electrolytic process and killing effect.
Sorry I'm not a chemist to be able to present ionic formulas and osmosis reactions, but being a very hands on manager at AutoPilot, I've seen, repaired and resolved many salt generator issues as well as pool water chemistry related issues (with and without salt sytems). I'm no expert by any means, but I do have experience and a little (dangerous) knowledge to get by.

Sean,

I wasn't clear with the amount of chlorine levels in the generator. I was talking about the normal operation that generates the incremental chlorine for the pool and referring to what some people were claiming was a natural superchlorination in the cell during this process. I was also referring to the entire cross-section of area that the water flows through and not just an area near the plates (which has incredibly high concentration of chlorine).

I believe what you are talking about is a superchlorination mode which runs the cell at a much higher power level. If you ran at this level during the duration of one pool turnover, then the pool itself would get to that 10 ppm level. Is this what you are talking about? I apologize for my ignorance about the mode you have for your cells.

Richard

No apologies, but thanks for "slappin me in the face" and making me aware that I sounded like a sales guy. That's the last thing I want to sound like here as it irritates Ben if I do.

The normal operation, when you inspect anyone's cell, is for the water to pass through and around the electrodes, or blades. Let's face it, the chlorine is only produced between the blades so the space around them does not get the same concentration of chlorine. However, it is quite high between the blades AND still quite high surrounding the blades too. Oddly, if you test the water coming out of the cell, you're prone to only get 1-5 ppm higher than what's tested in the body of the pool. You may see a similar result if you take a water sample from the closest return line to the pool equipment.
Now, the design of the cell is going to be rather different from manufacturer to manufacturer. If you inspect the various designs, you'll see different dimensions of blades, spacing between the blades, solid vs mesh, % ruthenium oxide coatings on the blades, and power (milliamps/sq cm) to the blades. So when you asked for more details, it's not easy...besides, most of this is proprietary information.

What I am taking about is not just under superchlorination mode, this is under normal operation. Besides, most Superchlorination mode does not increase the power to the cell, it simply extends the time the cell is energized. I believe there is only one manufacturer that claims to increase the output to 125%.
Most manufacturers cycle their cells on and off, during the day. Some run the cell continually, for a % of the pump run cycle (I'm not sure how this is determined without having to enter your physical pump run time). Some constantly energize the cell and fluctuate the power to the cell between a low output, up to a high output. Perhaps this last one is the model you're describing? Those are typical of Australian systems that also require higher salt levels to operate (4000 - 6000 ppm).

Hope this helps

I've been fascinated by this discussion and I'm continually trying to understand.

Are you saying that because the water "between the blades" is 80+ppm chlorine while the water exiting the cell is only 1-2ppm higher than the pool itself that the high CYA acts as a transport of that high chlorine? Sort of a way to get it into the pool?

That logic makes sense to me.....what Doesnt make sense is when Ben's best guess chart comes into play.

The chlorine in the pool, regardless of where it came from, has the same chemical properties as any other chlorine.

In my experience, when I ran my SWG at 80ppm CYA, my chlorine maintained at a lower power setting....as suspected. However, Algae on the walls and in the pool ran out of control and I fought it all season.
Ever since I lowered my CYA to 35-40ppm, I've not had to shock my pool once and haven't had a hint of "slimy walls" or the onset of algae.

There could be other factors at play since my tests were over the course of 2 seasons...

Yet my results are the exact opposite of Tredge. Running at about 30ppm CYA, I just couldn't keep my 30K IG pool "stable" (Aquarite). Every time I had any type of high bather load or lots of rain or a New York pollen "storm", the pool would get cloudy.

Now I am running at about 60 ppm CYA (I wonder if anyone can read the test more accurately than a 10ppm swing) and I have been able to scale back the SWG from 60 to 50 to now running at 40%. Water is clear and I am at about 4ppm FC. The pool is much more stable, it just stays clear and nice. It is possible that my results come from finally clearing out any residual "gunk" from opening, but I'm inclined to think it is due to running at or close to the SWG instructions.

Plus, my PH seems rock solid at 7.4/7.6.

Sean,

Yes, you've got my point. The fact that some small area of the cell and therefore some small percentage of volume of water going through the cell is exposed to 80 ppm of chlorine is interesting, but doesn't mean that all or even most of the water is exposed to that level except through many, many turnovers of the pool water.

An analogy with what happens when you add liquid chlorine (or bleach) to the pool might be helpful. Someone else [EDIT](let's give credit to waste where credit is due)[END-EDIT] mentioned this in this or another thread, but I'll describe the situation a little more deeply. When you add 6% bleach to your pool, you are adding chlorine in a concentration of 60,000 ppm. As the chlorine diffuses into the pool, at some point you will have the chlorine diffused into 1% of the total pool volume at which point the averge chlorine concentration in this volume of the pool will be 100 ppm assuming you added enough chlorine to raise the entire pool's chlorine level by 1 ppm. At a later point in time when the chlorine has mixed with 10% of the total pool volume, this volume has on average 10 ppm, etc. Now of course I'm oversimplifying since the mixing is not uniform (though I used the term "average" which covers up many sins) and there is not an absolute line of demarcation between pool water that has mixed with the chlorine vs. pool water that has not. But the principle is very much the same as what happens in the cell. Though some small amount of water is exposed to very high chlorine levels, it's still a small amount of total pool volume.

As an aside, the above "analysis" (and I use that term loosely since I was not at all precise in the above discussion) implies that it may be better to add liquid chlorine (or bleach) to the pool in a way that mixes rather quickly with a large volume of the pool water, but not with all of the pool water at once (which is impossible to do anyway). So adding the chlorine over a jet or into the skimmer may be better then putting it into one place in "calmer" water. I'm not sure how distributing it manually around the pool's entire edge would do, but personally I don't like to take that risk of splashing the 60,000 ppm chlorine onto my clothes!

Anyway, the bottom line is that I think that marketing a salt cell as somehow super-zapping your pool's water by using the high chlorine measurement example is telling the truth, but not the whole truth (I'm not accusing you -- you have been very forthright and honest in your discussions -- I'm talking about sales folks less knowledgeable than yourself). Unless there is good science to explain otherwise, what the salt cell does is not much different from what happens when you add liquid chlorine to your pool except that the cell is doing so continually over a longer period of time. It is possible that this is more optimal in producing the 10% volume / 10 ppm mix through the pool water. It is also true that the chlorine that is initially produced by the salt cell is unbound by CYA and therefore the true disinfecting chlorine concentration may be much higher, though the exposure time before this gets combined with CYA is rather short. Though the same thing occurs with liquid chlorine put into the pool, again the rapid nature of dumping chlorine in the pool is probably less optimal than the continous process of the salt cell.

Richard

Quote:

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Originally Posted by Tredge

Are you saying that because the water "between the blades" is 80+ppm chlorine while the water exiting the cell is only 1-2ppm higher than the pool itself that the high CYA acts as a transport of that high chlorine? Sort of a way to get it into the pool?
:
:
In my experience, when I ran my SWG at 80ppm CYA, my chlorine maintained at a lower power setting....as suspected. However, Algae on the walls and in the pool ran out of control and I fought it all season.
Ever since I lowered my CYA to 35-40ppm, I've not had to shock my pool once and haven't had a hint of "slimy walls" or the onset of algae.

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I don't believe the purpose of the high CYA is to "transport" the chlorine into the pool, but you are close to what I do believe is the purpose of the high CYA in making the salt cell more efficient. I'm going to try to explain this non-technically, but if I fail I apologize in advance.

The efficiency of the salt cell in generating chlorine is dependent on how much of this generated chlorine already exists near the generating plates. If there is already a lot of chlorine close to the plates that generate chlorine (due to its building up and not getting swept away fast enough), then the efficiency of the process drops and less chlorine is generated. The purpose of the CYA seems to be to combine with the chlorine that is generated and effectively "hide" this chlorine from the salt cell so that as far as the salt cell is concerned, the concentration of chlorine near its plates is not 80 ppm but something much less. The key to making this work is that the chemical reaction that combines the chlorine with the CYA to "hide" the chlorine needs to be faster than the production of the chlorine from the salt cell and it turns out that the critical point where this takes place is around the 60 ppm or so of CYA that is the minimum recommended by the manufacterer of the salt cell.

Your experience with algae is consistent with what I was saying in my earlier posts that Ben's chart is important to follow because the concentration of the disinfecting form of chlorine needs to be high enough throughout the pool, not just in pool water that passes through a salt cell. On the other hand, many people have reported no algae problems at higher CYA and Sean's experience is that those with lower CYA have had algae problems while those with high CYA have not, but that might have been due to the low-CYA cases having such low efficiency of salt cell chlorine generation that they couldn't produce enough FC to kill algae even at the lower level of CYA. At this point, I would say the jury is still out and my guess is that the continual dosing of chlorine from the salt cell is somewhat more efficient and does probably zap more bugs, oxidize more organics, and kill more *free-floating* algae than the manual dosing of liquid chlorine. That said, your experience shows that this greater efficiency of continual dosing from a salt cell is not enough and that you still need to have "Ben's chart" chlorine levels throughout your pool.

I do believe that it would be in the best interests of pool owners if the manufacturers of salt cells would at least consider the possibility that designing salt cells to operate at lower levels of CYA would be beneficial to "the rest of the pool" including pool surfaces where algae can develop (and bacteria can hang out in biofilms). All the salt cell makers have to do is simply increase the area of their plates over a larger volume and drop the power so that the local chlorine generation rates are lower since that will require a lower concentration of CYA to be able to "keep up" and "hide" the chlorine that is produced. And yes, this means that the salt cell may have to be bigger or, most likely, longer than it is today and that means more bulk and more piping to deal with this, but if it means a better situation for pool owners, then that's the right thing to do.

I just want to thank all of you that post on this and other threads. I have never experienced such a wealth and diversity of information and assitance in an environment that has remained civil. It's refreshing!

Richard

Richard & Poolsean,

This is so great for those of us on the edge of understanding it all. Its like reading Scientific America - I don't understand most of it but it sure stretches the mind.

The ONE thing that hasn't been addressed in your analysis, Richard, is the fact (using the term loosely) that almost everyone using a SWG with fairly well balanced water reports CC at 0 all the time. This is not true (I believe) of those that use bleach to maintain normal FC, at some point they will get a buildup of CC and have to shock (which is another interesting thread you are involved in!). This would seem to support the idea that the SWG is "super-shocking" in the cell and it must be some larger percentage of the water that passes through the cell than you are calculating.

In thinking about this though, you did say that it might take a couple of days to "shock" all of the water in the pool, perhaps this is happening and is "good enough" to keep the CC reading at or close to zero. I am wondering why or whether this information is available in Austrailia where they have been using these systems for a lot longer than here (at least for non-commercial pools).

A P.S. to Sean,

I seem to recall that the typical settings people are using with the salt chlorine generators is that they are on less than 50% of the time. Is it possible to have them on 100% of the time (when the pump is running), but operating at a much lower power level? Don't the lower power levels operate efficiently even at lower levels of CYA? If that is the case, then the simplest thing for owners of SWG to do would simply be to use the lowest power setting and increase their % on-time accordingly.

Of course, running at 100% means you have no leeway for the system to increase this if more chlorine is needed (due to increased chlorine demand), but if your system would instead just vary the power as needed (instead of the time) then this approach might work. What do you think?

Richard

I wonder if some of the problems that SWG owners have encountered with algae at recommeded CYA levels could be to either:
1) running at the low end of the recommeded 1-3 ppm FC levels
2) not keeping a good check on the pH and allowing it to drift upward too much before lowering it?
I maintain my pool at 3 ppm FC and do not let my pH rise above 7.6 (okay, MAYBE 7.8) before I add acid.
Also since my SWG does not compensate for temperature (Goldine Aqualogic PS-8) I do ajust my cell output if I see the chlorine levels are dropping or rising. (my pool has run on as low as 5% output in cooler weather up to 15% recently with my FC going up to 4 ppm)
I do test my water at least weekly (full tests except CYA and CAL) and do OTO and pH testing at least once more duing the week. Perhaps this is the difference in why I have never had any problems with algae. I test a lot of water at the pool store and I see that many owners of SWGs let their pH climb to 8.0 or above and never really get it down to where it needs to be. I also see these people having algae problems in their pools. On the other hand I had several customers with very low CYA (30 ppm and below) that were running their cells at very high output and also had algae problems and cloudy water in their pools. In both cases these people reported back to me that their problems seemed to disappear when their CYA levels and pH were brought into line.