Industry moving toward CYA at or below 50 ppm

[mikemass]

Yup - I can accept the consistency of dosing theory. But really how consistent is it? I run my pump for 8 hours a day. From 10am to 6pm. My normal cell use is set at 70%. So my "consistent dosing" consists of 5.6 hours of the day (.70 * 8 hrs = 5.6 hrs)

5.6 hours of a 24 hour day is consistent? I guess more consistent than adding bleach once a day. But if you add your bleach at dusk every night, one can make the argument, that the bleach is actually more effective as it has the nighttime hours to "do it's work".

I like the theory posted earlier in this thread that the concentration w/in the cell is so great that it annihilates everything that passes through it. But again, that's just a theory.

 

[JoyfulNoise]

It's not the high CYA in and of itself that I am expressing concern over. It's the statement TFP claims over and over again that you can run a lower FC level with a Salt system than you can with non SWG pools.

Let's say Powell's claim that the 7.5% guideline holds true. If I am running an 80 PPM CYA with salt, the Cl/CYA chart says I should run FC between 4 - 6. In %'age terms that is 5-7.5%

Needless to say I am going to err on the high side of that range for my piece of mind. Which actually puts me in the non-SWG range of 6 - 9ppm FC (7.5 - 11.25%)

What no one has addressed is why it is recommended to run a lower FC with salt at the same CYA than with non-salt other than: "It's just the way it is". Maybe in the archives of this site there is a sound reason to this. But everything I always remember reading is something along the lines: "It seems SWG users can get away with a lower FC." Even on the Cl/CYA page it states:

Please read this page carefully - Pool Water Chemistry

There is no "magic" associated with an SWG. The chlorine it produces is the same as the chlorine you get from a jug of bleach (minus the extra salt and lye). As well, both a 7.5% FC/CYA ratio as well as a 5% FC/CYA ratio produce an active chlorine concentration (HOCl) that is above the value which US and WHO consider standards for disinfection (bacterial and viral inactivation). Algae is a different story because (A) it's not a disease-causing pathogen so there's no accepted standard for the level of inactivation, and (B) it is a varied and complex aquatic organism that has a wide variation in chlorine tolerance. Some algae are killed in water with ~ 0.02ppm HOCl while other types of algae can tolerate HOCl levels above 0.1ppm. Ben Powell's "Best Guess Chart" was based on experience with a variety of many different pools expressing different algae types. Thus the 0.04ppm HOCl threshold seemed to conform the best with his predictions. As well, it was noticed that pools with SWG's could operate at lower HOCl levels than non-SWG pools. The explanation here is simply one of consistency in dosing. SWG pools are typically found with some kind of timer-based automation. Therefore an SWG pool gets a consistently applied dose of chlorine all day long. And yes, the cell environment is very harsh BUT that would only affect planktonic pathogens; anything stuck to the pips or on the walls of the pool will never see the inside of a cell.

In manually dosed pools, even the most OCD individual will have bad days or things happen that keep them from applying a dose of chlorine. Therefore it is entirely possible for a manually dosed pool to fall well below the HOCl threshold needed to keep water sanitary. As well, a manually dosed pool will have poorer FC distribution and have a spike in FC that deteriorates more quickly than a consistent low dose.

Therefore, because of the above differences, a manually dosed pool is asked to operate at a higher FC/CYA ratio simply to protect it from it's more extreme fluctuations in FC. I'm actually in the middle of an experiment where I am operating my SWG at less than the 5% FC/CYA to test out a few ideas. So far, no algae. I will release my findings and data at then end of the season because the data is incomplete. But the point of me mentioning that is because the FC/CYA ratio is an experimentally based concept that is grounded in the experience of ten's of thousands of pools. There is no one, simplified formula that controls chlorine-disinfection but rather a broad spectrum of possibilities. Pools will vary in their use of FC by type and region so it is important to come up with an operating point that works, and works simply, for the vast majority of pool owners.

As a final question: If exceeded usage of a Salt cell (running at 90+%, longer pump run times, etc) in order to maintain a higher FC as required with a higher CYA shortens the life of the cell, then why wouldn't I want to run a lower CYA, thereby maintaining a lower FC? Less run time, less output %'age on the cell = longer life?

Your thinking is wrong here. Running at a higher CYA allows your cell to work less, not more. Daily chlorine production of FC is controlled by the loss rate of FC per day, not the set point level. A clean pool has an FC loss that is entirely dominated by UV photolysis of hypochlorite. The higher the CYA level, the lower the daily loss rate and, by extension, the less run time required from an SWG cell. The primary moderation of FC loss from CYA comes from the buffering of chlorine by CYA. More than 90% of the chlorine is bound to the CYA (forming a chlorinated cyanurate) and only a much smaller fraction is the hypochlorite anion (OCl-). Therefore, because the concentration of OCl- is lower, the UV loss rate is lower. There is also a non-linear effect on UV loss from the CYA absorbing UV all by itself, but this process is not well established in the literature with any experimental data, it's just been noted that the protective effect of CYA is not simply accounted for by the lower OCl- levels so there is something "extra" that the CYA is doing.

You do not use an SWG to set the level, that is best accomplished by initially dosing a pool with bleach to get your to the correct level. You then use the SWG to maintain that level. This is why SWG's are basically useless when it comes to a SLAM and why we do not advocate using the "super chlorinate" mode on these devices.

 

[needsajet]

With automated dosing as the reason for the lower FC/CYA ratio in SWG pools, do pools with automated liquid chlorine dosing (e.g. Stenner pump, ORP based, or liquidator) exhibit the same tolerance for a lower FC/CYA ratio?

 

[woodyp]

I don't see us changing our recommended level of 70 to 80 CYA when a SWG is in use or the levels of FC for it.

 

[ned8377]

Also, it has something to do with how the water is super chlorinated as it passes through the cell and is able to kill everything because the chlorine level is much higher inside the cell than after it leaves the cell or gets out into the pool.

 

[mikemass]

With automated dosing as the reason for the lower FC/CYA ratio in SWG pools, do pools with automated liquid chlorine dosing (e.g. Stenner pump, ORP based, or liquidator) exhibit the same tolerance for a lower FC/CYA ratio?

I'd love to hear a valid answer on this. This theory makes perfect sense. A dosing type system that releases Chlorine at a steady rate throughout the duration of pump run time is the same concept of a SWG dosing during the pump run time. Seems to me that a Cl/CYA chart of a dosing pump should look similar to the Cl/CYA chart for SWG.

Also, it has something to do with how the water is super chlorinated as it passes through the cell and is able to kill everything because the chlorine level is much higher inside the cell than after it leaves the cell or gets out into the pool.

Yup - been mentioned twice already in this thread. I think this concept holds water (no pun intended). But then the same argument can be made for a dosing pump. Where the dosing pump introduces Cl into the system, wouldn't that area be "super-chlorinated" in the same fashion that the SWG cell environment is?

 

[mikemass]

Let me also add that since jacking my CYA up this year (higher than I have in the past), I keep lowering my %'age output on my SWG and notice I am still holding significant amount of FC. So far over the course of about a week of my high CYA I have reduced my salt cell from 90% to 70% to 50%. Still holding a 4.0 - 5.0 FC at this level. So, yes. I now see what you guys have been saying about my cell working less. After tonight's results, if I am still holding 4.0, I am going to try 30% and see what that does.

 

[ned8377]

Here is some more information from the CDC about the relationship between FC and CYA. If you read this entire document, one page PDF, including the footnotes, you will see that high CYA slows down disinfection times and especially slows down the killing of Cryptosporidium parvum. Admittedly Crypto in a residential pool is unlikely but maybe this is part of the reason CYA ppm recommendations are coming down.

https://www.cdc.gov/healthywater/pdf/swimming/pools/hyperchlorination-to-kill-cryptosporidium.pdf

 

[JoyfulNoise]

Here is some more information from the CDC about the relationship between FC and CYA. If you read this entire document, one page PDF, including the footnotes, you will see that high CYA slows down disinfection times and especially slows down the killing of Cryptosporidium parvum. Admittedly Crypto in a residential pool is unlikely but maybe this is part of the reason CYA ppm recommendations are coming down.

https://www.cdc.gov/healthywater/pdf/swimming/pools/hyperchlorination-to-kill-cryptosporidium.pdf

If you look at the abstracts of the papers cited in the reference, you'll see a lot of talk about how CYA reduces the efficacy of chlorine inactivation. I do not have access to the details of the data but it seems to me that the authors are surprised by something that is obvious - CYA lowers the active chlorine (hypochlorous acid) levels. All of their data talks about the FC levels needed to achieve specific CT inactivation values. But none of that is normalized to the parameter that matters - HOCl concentration. It is HOCl that is the primary disinfectant that kills pathogens. So, in order to do a complete analysis, one needs to actually calculate the HOCl concentrations as a function of CYA and pH (you know, actually do the equilibrium chemistry analysis) and then plot CT inactivation as a function of that. They state that all of their tests show that the kill times when CYA is present is always lower than the chlorine only controls...well, duh, that's because CYA strongly moderates the amount of HOCl available.

In general though, and as you state, this advisory document has little to do with residential pools since crypto is pretty rare. One would have to have an active crypto infection and then have a fecal accident in the pool water for this to be of any concern. I've been operating my pool for several years now and I have never had any "fecal accidents" in my water....

 

[AUSpool]

With automated dosing as the reason for the lower FC/CYA ratio in SWG pools, do pools with automated liquid chlorine dosing (e.g. Stenner pump, ORP based, or liquidator) exhibit the same tolerance for a lower FC/CYA ratio?

I've been eagerly waiting for someone's response to this. Initially I thought yes but the more I thought about it the more I think the opposite, mostly due to a one recommendation to suit most pools perspective where dosing systems can all be a little different with user adjustable settings for both dose and time. Automated dosing systems have a different dosing per time profile, a SWG has a constant output throughout the duration of the run time while a dosing system is more on/off and maybe a bit more prone to failure or change over time. If a FC/CYA ratio was to be assigned to automated dosing systems I think it would probably be somewhere between a manually dosed pool and a SWG pool but maybe closer to a manually dosed pool? - just my thoughts.

 

[needsajet]

I'm waiting for this as well, AUSpool. I most certainly do not believe in magic occurring inside an SWC, but it does make sense to me that there could be a beneficial effect arising from the harsh environment inside the cell housing. Conversely, it also makes sense to me that it's strictly about consistent dosing, particularly given that not all the pool water goes through the SWC, but there are some gaps to consider.

I recently learned that either Pentair or Hayward (forget which) SWCs use a 3-hour cycle time. So if they're running at (e.g.) 30%, they dose for 54 minutes and then they're off for 126 minutes. That's not quite what I'd call steady dosing, and it's possible to set this even higher to 5 hours. Just mentioning this because I think it's fair to say that the "steadiness" of SWC dosing varies as well, in the same way that Steve mentions with respect to liquid dosing. My SWC cycles every 10 minutes, so that would be 3 minutes on, 7 minutes off, which seems more like steady dosing, with the timing of polarity reversal based on an accumulation timer.

For completeness, I haven't heard a solid answer on this. I've asked if there's a sub-timer in the Pentair/Hayward SWCs that's switching the cell on and off more frequently within this 3 or 5 hour window, and the language keeps coming back in a way that could be interpreted either way. Hayward, for example, just says 54 minutes producing chlorine and 126 minutes not producing chlorine (at 30%).

But beyond that aspect, there's a fair number of people who run their SWC at night because of lower power rates. In that case, dosing of chlorine while algae is most active is not happening at all. This group would experience the same daily losses and FC fluctuation as someone who doses with liquid bleach every evening.

 

[Lykly]

needsajet:
From what I understand, the Hayward runs on a three hour cycle as you mentioned above. I just recently raised my CYA up as well.......



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[AUSpool]

In general though, and as you state, this advisory document has little to do with residential pools since crypto is pretty rare. One would have to have an active crypto infection and then have a fecal accident in the pool water for this to be of any concern. I've been operating my pool for several years now and I have never had any "fecal accidents" in my water....

Cryptosporidium parvum is a mammalian intestinal protozoan parasite, humans, dogs, cats, bats, rodents, so could be more common than some of us would like, but still pretty rare. Some pools would obviously be more subseptable than others and according to the wiki it can survive for 24 hours at 1000ppm FC so I guess it's probably a bit useless to treat a pool for it although I suspect it is only the oocysts that are resistant to those levels. Luckily protozoans, including crypto and giardia are quite a big parasites which is why I filter my drinking water to 0.5 microns.

 

[JoyfulNoise]

I've been eagerly waiting for someone's response to this.
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I'm waiting for this as well, AUSpool...
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From what I understand, the Hayward runs on a three hour cycle as you mentioned above. I just recently raised my CYA up as well.......

First off, I would check on that cycle time parameter...pentair uses a 1-hour cycle time, so that is 24 cycles/day. My understanding was that Hayward used a slightly longer cycle time so that they have 20 cycles/day. You may be confusing the 3-5 hr timing for the periodic polarity reversal of the current. For Pentair, the polarity reversal is selectable from 3, 4 or 5 hours. The ICs are programmed to start out with a reversal cycle of every 3 hours for the first 30 days and then it lengthens out to 5 hours.

As for Stenners versus SWGs, I think you guys are on the right track. Let's look at the cases -

Case #1: Manual Chlorination

Manual chlorination involves a relatively "huge" concentration of liquid chlorine all at one specific time (most people manually chlorinate at night). This method is the most sensitive to variation because first of all it relies on a person doing the chlorination. Life happens and no one is perfect so manual chlorination is subject to a lot of user error (bleach strength off, improper amount of bleach on hand, too little/too much poured in at once, etc, etc). It's also a large concentration of LC that is more apt to not fully mix if the pool pump is not running for an extended period of time after dosing. I believe manual chlorination is much more prone to developing dead spots due to poor circulation patterns and ineffectual mixing.

Case #2: Stenner Pumps

Peristaltic injection of LC attempts to get around the human factor a bit by automating the injection of chlorine. However, from a time/dose perspective, Stenner pumps still inject a "huge" dose of chlorine into the pools plumbing system over a very short period of time. Correct me if I'm wrong, but most Stenner owners program their injections to last, at most, less than hour as many people try to cut down on pump run time. Stenner injection is also going to be subject to circulation issues but it certainly has a much better chance of achieving uniform distribution. Bleach concentration, pump failures, etc, are all still a concern.

Case #3: SWG's

SWG's remove two factors - human failure and chemical variation. Also, the time/dose profile of an SWG is a lot slower than either peristaltic or manual injection of chlorine. SWG pools typically run their hydraulic systems for much longer periods of time than do manually dosed pools. So, when chlorine is generated, it is added to pool more slowly and over longer periods of time. I believe this has a tendency to create better distribution of chlorine in a pool's water volume. As you have noted, the inside of an SWG cell when it is generating chlorine is very harsh - the pH (without borates) can easily rise well above 10.5, both oxygen gas and hydrogen gas is evolved leading to an incredibly corrosive and toxic environment for biological entities. Not all of the water volume is treated to this harsh chemical effect, but none of the other chlorination methods can produce this effect. Certainly cell failure and decreased efficiency due to scaling is a concern but modern SWGs have come a long way since their initial offerings.

One other thing to keep in mind is that, as you say, there is no magic here. The FC/CYA ratio is an empirically derived value based on the equilibrium chemistry of chlorine and cyanuric acid as well as the experience of actual pools. The FC/CYA ratios used by TFP (5% and 7.5%) certainly create levels of hypochlorous acid fully capable of killing most pathogens and oxidizing organic compounds. Algae, comparatively speaking, is a slow growing nuisance (not really a pathogen, per se) and sanitized pool water has very little algae in it to start with. So even though the active chlorine levels required to kill algae are quite a bit higher (and algae, in a general sense, is all over the map in terms of chlorine sensitivity), the ratios we recommend are more than adequate too keep up with it. I believe the driving force behind the lower ratio for SWG pools is as you surmise - there is a much greater chance for variation in FC levels with a manually dosed or peristaltic-dosed pool than there is with an SWG pool. The variation is enough to warrant a higher overall dose so that accidents don't lead to cloudy water. Could a Stenner pump be set to dose in a fashion similar to an SWG? Sure, but that would defeat one of the benefits of a Stenner pump, namely the decoupling of chlorination from pump run time. So any money you save by dosing at a "low and slow" rate while using a lower FC/CYA ratio may be entirely offset by having to double, or even triple, pump run times.

Cheers,
Matt

 

[needsajet]

Fair enough, let's remove the Hayward cycle time. I did check this as I mentioned in the thread, both from Hayward and an expert here, but that can certainly be set aside.

How about these questions?

Is there a body of evidence that pools equipped with liquid chlorine dosing, and which dose periodically throughout their pump run time, are able to successfully reduce their FC/CYA ratio to a similar level as that used with SWCs?

And/or
Are SWG users who run their SWG only at night also able to reduce their FC/CYA ratio to minimum 4.5% and have similar success as those who run their SWG during the day?

And I think this is also important:
How many SWC users run their pumps longer than needed for circulation and filtration, strictly to enable adequate SWC time? I've certainly run into a few with small SWCs, so I can accept the importance of the variable, but I also think most people understand the need to install a big SWC (to improve both SWC and pump run time economics).

My understanding is that the FC/CYA ratios are empirically derived values based on experience gained from many actual pools. In addition, and one of many things that drew me to TFP, were the brilliant descriptions and explanations provided by Chem Geek about why the values work, based on the equilibrium chemistry of chlorine and cyanuric acid.

So maybe we have an opportunity to honor the tradition of finding methods that work. A survey of Stenner users with both run time description and successful FC minimums and targets might provide a body of evidence. To some degree at least, we could test whether or not it is only consistent dosing that allows the lower FC/CYA ratio experienced in SWG pools. One of Chem Geek's posts covers this topic, and in his usual concise yet thorough style he mentions that not enough is known to explain lower successful FC levels in SWG pools, and that the ability to test and measure what's happening inside a cell housing is, at the least, a challenge. But if evidence suggests that it's purely dosing, then we would have a new tool to offer pool owners with liquid chlorine dosing.

 

[Lykly]

You may be confusing the 3-5 hr timing for the periodic polarity reversal of the current.

I can't speak for anyone else, but Matt you are correct, that is what I was referring to from what the Hayward tech told me. Sorry for the incorrect input on my behalf.


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[JoyfulNoise]

Is there a body of evidence that pools equipped with liquid chlorine dosing, and which dose periodically throughout their pump run time, are able to successfully reduce their FC/CYA ratio to a similar level as that used with SWCs?

Not that I know of.

Are SWG users who run their SWG only at night also able to reduce their FC/CYA ratio to minimum 4.5% and have similar success as those who run their SWG during the day?

Running at night simply removes the UV loss component. So running at night might let you run the pump/SWG less to produce the same amount of chlorine as you wold during the day since you are now not fighting UV photolysis. However, you need to run the chlorinator long enough to produce enough FC at the beginning of the day so that you end the day above the minimum FC. I'm not actually sure this would be very beneficial as the pool would now look more like a manually-dosed pool, i.e., a big FC load upfront and then let it burn off throughout the day.

As well, FC dosing schedules have little to do with the FC/CYA ratio. I know that TFP uses two different recommendations, but it's because of the way chlorine is dosed and the amount of human error involved in that process. There is no chemistry/scientific reason for it, it's simply a matter of giving people more of a margin to make mistakes in and not have a catastrophic result. There are people (and I think you know who) who can manually chlorinate their pools and use a FC/CYA ratio that is half of what TFP normally recommends. But the reasons for that have more to do with the chemical nature of the water and the way pool is operated (low nutrient, covered, etc), not with the dosing schedule.

How many SWC users run their pumps longer than needed for circulation and filtration, strictly to enable adequate SWC time?

This is almost universally true for SWG pools. Pump runtime studies (ask mas985 for the details) have shown that most residential pools only need to run their filtration system for a few hours per day (4 hours or less) to achieve what most consider to be a "clean" pool. The concept of needing a specific number of turnovers is outdated and untrue. Low pump runtimes for filtration is even more apparent if one uses a robotic cleaner since the cleaning cycle can be decoupled from the pump runtime (my next big pool purchase will be a robot cleaner!!). In salt-water chlorinated pools, the pump runtime is entirely dominated by the need for chlorine production. I did a quick spreadsheet about a month or so ago that showed pretty clearly that most pools (15k gallons and larger) will run their pumps about twice as long as needed relative to basic water filtration needs even when the SWG is upsized by a factor of 2. So one can say that SWG pools have water that is certainly over-filtered.

So maybe we have an opportunity to honor the tradition of finding methods that work. A survey of Stenner users with both run time description and successful FC minimums and targets might provide a body of evidence.

Feel free to start a survey thread in the Automation sub-forum. It would be interesting to know how Stenner pump owners operate their systems and what results they get. The "Best Practices" information gathered could even make it into a Pool School article to help new users who desire to switch to chlorine injection.

 

[Schadenfreude]

My two cent on SWGs:

My SWG is the last thing the water goes through before it re-enters the pool. It enters through 10 wall returns and 4 floor returns, so it is instantly distributed throughout the pool almost completely and reasonably evenly. You just can't get this pouring it in front of a single return, even in a relatively small pool.

In addition, and I suspect one of the most important parts, freshly chlorinated water is pumped through all of the pipes and plumbing for all of those 14 returns. I keep my pool at 6 ppm, so I think the water running through the pipes will be a bit higher than that, perhaps 8 or 10 ppm. This eliminates hiding places for bacteria and spores that might occur in a regular pool. Keeping chlorine higher in a non-salt pool is probably necessary to properly sanitize these hidden areas.

 

[AUSpool]

It looks to me that the industry has been at 30-50ppm for CYA for a while, or at least some parts of the industry. I have an old pool guide (2005) produced by Hach that quotes a 1999 IAF/NSPI standard for CYA at a minimum 10ppm, idea at 30-50ppm and max at 150ppm. No correlation between CYA and FC. A bag of isocyanuric acid I have quotes an ideal range of 30-50ppm with no correlation between CYA and FC.

My target is 70ppm/5ppm but after playing with a new CYA view tube where I was consistantly coming up short I thought of maybe setting it at 60ppm/5ppm but in reality I'm not really changing, just assuming my real value is a little higher then my tested value. While pondering that I went back over the TFP recommendations for a SWG pool and the 60/3-4 value is not recommended but it doesn't say why. Anyone know why?

 

[needsajet]

Steve, I followed a discussion about that elsewhere, and the higher CYA recommendation for SWG is related to reducing cell run time, thereby extending cell life and reducing upward pH drift, but not sanitation. Sanitation is considered to be fine at lower CYA levels, provided the 4.5% bare minimum is respected.

You can find older threads here mentioning that manufacturers know their cells are marginally more efficient at higher CYA, hence their traditionally higher recommended levels.

Likely the larger advantage is that for both SWG and non-SWG pools, a higher CYA level reduces daily chlorine replacement, all else being equal.