CYA / Pool Pilot Question

[ohpoolboy]

I live in the Northeast so my pool is not subjected to the high temperatures and scorching sun that others experience. I have a Pool Pilot SWG that maintains a 2.0 ppm FC while the CYA is 0. (ph = 7.5 ALK = 80 Water Temp = 80). It really does not fluctuate that much. I've tested it in the morning, afternoon and evening.

Pool Pilot recommends a CYA of 60-80. According to Ben's best guess chart this would require about 7-8 ppm of FC.

Here's my question:

If I raise the CYA to 60-80, will I have to raise the power setting on the Pool Pilot to achieve 7-8 ppm? Right now it's operating at 60% @ Power Level 2. As I understand, the higher the power setting, the shorter the life of the cell.

-OR-

Will the increased CYA allow the Pool Pilot to achieve those numbers without a significant power increase?

I guess I'm a little gun shy when it comes to adding CYA since it can only be lowered by draining the pool. I also like the fact that the SWG is at 60%,which is in the range of what the manufacture recommends.

[cwstnsko]

The importance of CYA is purely a function of the need to protect chlorine from the sun. If you don't get much sun and you are not seeing the chlorine drop during the day, you may be fine. If you are indeed using a higher setting on the SWC to compentsate for Cl loss to the sun, your trade-off is cell life, and the fact that Autopilot might not honor their cell warranty if you run w/o CYA.

I ran my SC-48 cell with low CYA and output at about 40%(24/7) and I had a cell fail in less than 2 years (17000 amp-hours of use according to the controller). Luckily for me, Autopilot replaced it under warranty, but I run about 30 ppm CYA now and run the output lower

Most of the quasi-scientific looks at CYA seem to show that the majority of the benefit is realized in the 1st 10-20ppm CYA. A little CYA might yeild measuable cell life gains without compromizing sanitization too much.

[ohpoolboy]

Thanks for the reply. That's exactly the type of information I was hoping to get. :)

[JohnT]

I think the best guess table doesn't apply completely to SWCG pools due to the continuous "shocking" action in the chlorinator chamber.

[waterbear]

Actually, if you raise your CYA to the recommended levels you will find that you can turn the output of the cell down....not up! Both PoolPilot Systems and Goldline Controls have said that the reason for the high CYA levels is more or less because of the way the chlorine is introduced into the pool at extremely high concentration in a small volume of water within the cell. It would appear that the best guess chart does not apply to SWGs for this reason since most of the people on this forum, including myself, report very good results with the CYA in the recommended range and FC levels of around 3 ppm. BTW, DO NOT go below 2 ppm. This has noththing to do with SWG but has to do with the necessary levels of chlorine needed to kill waterborne pathogens based on recent studies!
I myself was skeptical about running the high CYA levels with my SWG at first but found that the unit actually operated better with a more constant chlorine level and at a lower power setting then whem my CYA was at about 40-50 ppm!

[mas985]

My experience was a bit different than Evan's. I increased my CYA from 30 to 70 ppm and did not see a rise in CL residual for the same settings so I was unable to turn down my SWG. Our different results could be due to the size of pool, UV exposure or other factors. So I think it really depends on the conditions of the pool as to need of high CYA.

One thing I found useful during my expermental rise with CYA was to calculate how much CL was going into the pool per day. I know how to do it for the Goldline SWG but not sure for the poolpilot. Sean should know. Anyway, I found I was putting in 2 ppm per day and my residual was at 2 ppm. So based on that, I probably should not have bothered adding more CYA but I wanted to try it anyway. So if your residual is much less than what you are putting in per day, then I would say you probably need more CYA.

[chem geek]

I would be somewhat skeptical of the claims of superchlorination with SWG systems. Yes it's true that the concentration of chlorine generated in the cell is higher than the average you end up with in the pool, but if you do a little math you can see that the chlorine levels in the cell are not as high as implied by the manufacturers.

First of all, Ben's chart refers to chlorine levels that must be maintained throughout your pool in order to disinfect and prevent algae. Now any superchlorination done at the cell (more on that below) may disinfect more, but unless your pool turnover is very fast, it is likely you won't "disinfect" your entire pool in less than several hours. Also, both bacteria and algae can stick to and grow on pool surfaces (in what are known as biofilms) where the superchlorination in the cell does absolutely no good at all.

If your normal 60% operation setting means that the cell is turned on 60% of the time and you maintain a 2.0 ppm chlorine level at this setting, then if we assume a turnover rate for your pool (i.e. how long it takes for your entire pool's volume of water to go through the pump and chlorinator) of 4 hours and a chlorine loss rate of 1 ppm per day, and that your pump (and chlorinator) is on 8 hours/day, then your chlorinator is introducing 1 ppm of chlorine over 24 hours which is 8/4 = 2 turnovers so that is 1 ppm in 2 pool volumes or 0.5 ppm actually being introduced -- divided by 0.6 for the time the cell is on gives 0.83 ppm.

Yes, this means that your "superchlorination" is simply having 2 ppm chlorine enter your chlorinator and 2.83 ppm leave it. That's not very much.

If you think about it, any chlorinator that is turned on 60% of the time couldn't be introducing huge amounts of chlorine into the system because if it did, you would end up with that large amount of concentration in your pool in about the turnover time (ignoring the chlorine loss over that time which isn't huge in your case).

Now in the above discussion I have assumed that all of the pool water goes through the chlorinator. I don't have a chlorinator so I don't know if they are installed in a "bypass" fashion such that only a portion of the pool water goes through the chlorinator. If that is the case, then the chlorine levels would be higher by the inverse fraction of the amount of water that goes through the chlorinator, but then it would take even longer for the entire pool's volume of water to get "exposed" to such superchlorination (and as I said before, that doesn't help bacteria and algae stuck to pool surfaces anyway).

Now, back to your CYA issue. Use Ben's table. The fact that you are using an SWG system is not relevant. You still need to use Ben's table. Since you are not losing a lot of chlorine, you can use a lower level of CYA so that your 2 ppm of constant chlorine will work. That means using about 10-20 ppm of CYA though my calculations show that you would be fine at 20 ppm of CYA. Of course, most test kits only measure down to 30 ppm CYA (a few kits measure down to 20), but since you don't have extreme sunlight you can probably get away with less CYA that even your test kit can't measure (just make sure it looks cloudy even though you can still see the black dot) and make sure that your chlorine levels are maintained, especially during the peak of the sunlight part of the day (near noon?).

[EDIT]A little CYA goes a long way as shown in the following graph Halflife.gif (http://richardfalk.home.comcast.net/pool/HalfLife.gif)
You don't save that much chlorine by adding more CYA beyond a relatively low level, but you significantly increase the need for higher Free Chlorine (FC) to maintain disinfection and algae prevention. Another way to look at it is with the following graph ChlorineLoss.gif (http://richardfalk.home.comcast.net/pool/ChlorineLoss.gif) which shows that at constant disinfecting chlorine (HOCl) levels, lower CYA has a lower absolute rate of chlorine loss and therefore a lower absolute rate of chlorine generation need from your chlorinator. Ironically, you optimize the use of your chlorine generator if you use absolutely no CYA at all. Yes, this is counter-intuitive but is true because the chlorine tied up by CYA still gets broken down, though at a much slower rate, and yet it does virtually nothing for disinfection or algae prevention. The chlorine tied up by CYA is simply a reserve of chlorine -- nothing more. So by using CYA, you are simply having an additional, and rather large, reservoir of chlorine that must be maintained and in fact is where most of the chlorine loss comes from (except at very low levels of CYA). This does not mean, however, that you should not use any CYA at all because the graph assumed that with no CYA you would maintain throughout your pool a chlorine level of, say, 0.05 ppm which is not realistic. From a practical point of view, you would have at least 1 ppm of chlorine in your pool so that implies a CYA level no greater than about 10 ppm. Since you are already at 2 ppm of chlorine, you should not have your CYA level higher than about 20 ppm. Again, use Ben's table, but my advice to maximize the life of your cell is to use the lowest level of CYA that is practical for measurement and for having a decent minimum FC level in your pool. An FC of 2 ppm is reasonable since this gives a decent buffer to handle areas of "less than ideal" circulation plus localized introduction of ammonia and organics from bather load (sweat and...). The reason Ben promotes a high-CYA/high-FC combination is to have a sufficient buffer of chlorine to ensure that you never, ever get to dangerous levels in manually-dosed pools. In a pool with an automatic chlorinator, this is far less a concern, though you should make sure that your FC never drops below the minimum level (say, 2.0) even during times of the day or night when your chlorinator is not operating (i.e. set your chlorinator to a higher FC level when it is on so that the worst-case when it is off is 2.0 FC).[END-EDIT]

Richard

[mas985]

Richard,

This has been debated many times before on poolforum and I believe that there is a difference between a SWG and manual chlorination which Ben's table was targeting. Here is one of the more recent debates if you are interested:

http://www.poolforum.com/pf2/showthread.php?t=3185

Many SWG users operate 60-80 ppm of CYA and 2-3 ppm of chlorine, including myself, and do not have a cloudy pool or algae that many others who post on this forum do. So although there is some speculation on exactly what is going on in the cell, besides the generation of chlorine gas, the manufacture's recommended CYA and CL levels seem to do the trick.

One more thing, from the analysis you did in the China Shop, you showed that you only need 2 ppm CL for a CYA of 70 ppm to kill bacteria, assuming 0.01 ppm HOCL. Also, given that it takes awhile to produce algae, a slow kill in a SWG, even over several days, may be sufficient to keep the water clear. This may help explain the difference between SWGs and manual chlorination.

[chem geek]

Mark,

Thanks for the link to the discussion. Ben's chart is conservative, partly because it is for manually-dosed pools where the chlorine level fluctuates so "could" get low at some point. The accurate relationship between disinfecting chlorine levels and the amount of FC and CYA in the pool is calculated in the following chart FC.htm (http://richardfalk.home.comcast.net/pool/FC.htm) and graph HOCl.gif (http://richardfalk.home.comcast.net/pool/HOCl.gif)

Ben's table roughly correlates with this data, at least for his minimum and maximum FC ranges (the shock area is another matter, but we are still figuring that out). I can say with reasonable confidence that the 0.011 ppm HOCl level is a minimum level needed for disinfection in a commercial pool environment, but it may very well be that in a home environment it simply isn't that big a deal if a bug is killed in minutes or even hours compared to seconds if it's just your own family in the pool (and one should note that even the 0.011 ppm HOCl level does not kill hard-to-kill bugs). Nevertheless, if you look at the 0.010 column in the chart, you can see that you can most certainly run at much lower FC levels with higher CYA levels. So for minimum disinfection this makes sense. Even 80 ppm of CYA at 2 ppm of chlorine gives an HOCl level of close to 0.010. ([EDIT]Oh, I see you said that in your post -- sorry for not getting that the first time :( [END-EDIT])

What is not so clear is what is required for algae prevention. Ben has seen pools develop algae even when the HOCl level (that I calculated based on the FC and CYA he mentioned) was just under 0.05 and the middle range of his table is roughly in this area. So it would be interesting to figure out if and why SWG pools running at 70-80 CYA and 2-3 ppm chlorine don't get algae. [EDIT]Your explanation of slow algae growth with some superchlorination through the salt cell sounds reasonable except for algae that grows on pool surfaces and doesn't pass through the cell. Maybe for some reason the algae in salt water needs less chlorine to prevent it from growing. Of course, I always thought algae liked salt (e.g. ocean).:) At any rate, the determination of algae prevention and algae kill (shock) levels both for non-SWG and SWG pools is something I want to try and figure out using the resources of this poolforum. I plan to start a thread for that purpose sometime soon. Thanks for your input.[END-EDIT]

As far as what level of CYA is appropriate, it is true that once you figure you want to run your pool at 2-3 ppm, then higher CYA levels will reduce the chlorine loss. Remember that my argument was the other way around -- setting a disinfection level and then determining the level of CYA needed for that level. The loss rate of chlorine at 2 ppm FC in sunlight with 80 ppm CYA is about 0.187/hour while with 40 ppm CYA it's about 0.210/hour so this isn't a very big difference, but the disinfecting chlorine (HOCl) level at 80 ppm CYA is only 0.010 ppm compared with 40 ppm CYA that produces 0.020 ppm or twice as much disinfecting capability. That was the main point I was trying to make. A little CYA goes a long way so I believe having your salt cell work 12% more to get twice the disinfection and algae prevention capability is worth it. [EDIT]Some of the posts in the link you gave indicate that the lower CYA required cells to work much more than the 12% I stated, but they also said they had algae problems which doesn't make sense unless they couldn't keep up. waterbear reported some of this so I'll try and get more info and see if we can figure this out. The most logical explanation I saw, so far, was the one that CYA helps assist in the chlorine generator cell itself to prevent some chlorine from breaking down under the high concentrations.[END-EDIT]

Richard

[Poolsean]

Mark,
What is your cya level currently? It would be interesting to see what would happen to your chlorine demand if you lowered your cya back to 30ppm. Or do you normally operate at 60 - 80 ppm and then tested the effects by dropping down to 30 ppm?
You stated in your post today "Many SWG users operate 60-80 ppm of CYA and 2-3 ppm of chlorine, including myself, and do not have a cloudy pool or algae that many others who post on this forum do." but in the post you sent the link to (your post dated 6-22-06) you stated "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."

As a comparison, my 20,000 gallon outdoor pool @ 70 - 80 ppm cya was operating last year with my Pool Pilot at about 30% output, 6-hrs per day with my SC-48 cell (max output = 1.56 lbs/day) and was maintaining 2-3 ppm (as tested with the Taylor K-2006 test kit). I kept pH at about 7.5 - 7.8 by manually dosing acid. I converted to the Total Control system back in Aug of last year and get about a 22% utility reading (which equates to about a 22% output setting), all other parameters the same as before the Total Control but with pH @ 7.3 electronically controlled.

FYI, the 1.45 lbs/day you're using to calculate your chlorine and ppm are swayed (no offense). This is a number that iwas submitted to NSF for testing under "IDEAL" conditions, which are not usually real world conditions.
Such as indoor (no UV), cooler water temps, higher salt levels, no bather loads(or chlorine demands), and most importantly, lower flow rates.
How does NSF validate the output claim? They start with a known free chlorine base level (no chloramines), run the systems, take periodic water samples, and tests for free chlorine. So as the salt system generates at full output, NSF records the free chlorine, calculates the increase per hour for the 24 hr period, then determine the max output. They repeat this several times to confirm consistent output.
The question is this, what does a manufacturer actually submit as the operating parameters to get the max lbs/day output?

I cannot dispute your test results for your pool. However, I think Waterbear and I both see many more backyard pools (water samples in his case) to state with certainty that the higher Cya levels do allow you to decrease the output of "a" salt system and still maintain a safe and clean pool.

Man, I can see this heading to the China Shop...

But let me state this. The Salt Chlorine Generator industry have NO vested interest in cyanuric acid sales, so we're not claiming a high-er cya is needed, just for profits. It's quite the opposite. We know from experience, that Cya helps to protect the chlorine from the sun's UV rays, not just from the heat of the sun. While you can get away with maintaining lower cya in a salt pool, your cell will suffer as a result.

Interesting article on UV radiation.
http://yourskinandsun.com/article1072.html
Northern climates may justify maintaining a lower cya due to it being further away from the equator, thus less UV exposure. But climb into the mountains and you should require a higher cya level.

Ben, have you ever read this article? I'm not a chemist by any means so any of you chemist types that disagree with this paper, please feel free to educate me.
http://www.magma.ca/~dougdela/chemed03/pool1.pdf
I do see that he states anything above 50 ppm cya is of little effect...darn it. Well, it's not just debated here. It is debated within the industry itself.
Just a worthy note, most Department of Health limits commercial pools to 100 ppm. More recently lowering that to 80 ppm. In fact, NY State does not permit CYA, except for special circumstances, such as outdoor pools, where pool operators can request the special exception to use it. In speaking to several of these pool operators in northern NY, they see the tremendous cost savings when permitted to use cya. Guess what level they maintain? OK...50 to 60 ppm. Not quite the 60 - 80 ppm we recommend, but not quite 30 ppm either.

...and so it continues...

[chem geek]

Sean,

I moved my conversation over to the
CYA for Salt Chlorinator Pools (http://www.poolforum.com/pf2/showthread.php?p=27887#post27887) thread, but at the end of this linked post I mention how I did some rough calculations that, somewhat to my surprise, justify the theory of higher CYA levels making the salt chlorine generator cells more efficient.

To more fully validate the theory, I need some basic parameters of information such as cell chamber size, plate size, typical water flow rates through the cell, etc. since my estimates were pretty much guesses. It sounds like you're a sales guy, but if you can get your technical folks to help out (unless you know this information), I'd really appreciate it. Rather than bore the heck out of the people on this forum, you can send any information directly to me via E-mail since I allow that (just click on my "chem geek" name to get to my profile where you can send an E-mail). I can then post my net results that I expect will confirm what my very rough calculations have verified.

It's funny how the whole thing pretty much hinges on the rate constants (which I have) for the taking up of chlorine by CYA and how this gives half-lives in the sub-second ranges that roughly correspond to the time water spends inside the cell. I truly didn't expect that -- funny how even someone like myself who believes in the power of science still gets amazed when something that *should* come out a certain way actualy *does* come out that way.

[EDIT]By the way, making your cells larger (longer) and breaking up into multiple plates with space between them (or using multiple cells running at lower "power" generation rates) would let people use lower levels of CYA. The key is to give the generated chlorine time to combine with CYA and not build up too much in concentration. So a multiple staggered plate design would also work (but alas, is more complicated). Just giving you food for thought.[END-EDIT]

Richard

[Poolsean]

hmmm, not sure if to take offense at your comment...
"It sounds like you're a sales guy, but if you can get your technical folks to help out (unless you know this information), I'd really appreciate it. "
Ouch...all my efforts of being unbiased and informative, and I get called a sales guy. Back to the ole' drawing board.

I also posted on the other link. I'll move to that one too.

[chem geek]

hmmm, not sure if to take offense at your comment...
"It sounds like you're a sales guy, but if you can get your technical folks to help out (unless you know this information), I'd really appreciate it. "
Ouch...all my efforts of being unbiased and informative, and I get called a sales guy. Back to the ole' drawing board.

I also posted on the other link. I'll move to that one too.
Sean,

As you have figured out from my posts on the other board, no offense was meant and my wording was poor. I'm sorry about that.

Richard