Should I increase my CYA levels

[peterl1365]

Okay, new pool, filled with water for about 6-8 weeks now.

My CYA levels are testing at between 30-40 ppm. I have a Pentair Intellichlor IC40 SWG. The IC40 manual recommends a CYA level of between 50-80 ppm.

So far, I haven't had any trouble maintaining FC levels. The IC40 has been running at between 4 and 6 percent. The pump runs at very low speed about 20 hrs per day and at moderate speeds (2100-2500 rpm) for about 2 hours a day for vacuuming and surface skimming. As the weather gets warmer and the sun more intense, I figure I may have to bump the SWG to maybe 10% or so.

Given the above parameters, is there any reason that I should increase the CYA?

 

[Guest]

IMHO, bumping up the CYA will increase your cell life and help reduce the possibliilty of combined chloramines forming. . It would be helpful if you posted a complete set of test results including pool temperature. If the water is on the cold side and you are maintaining a FC between 3-5 ppm then I suspect you will need a higher FC once it warms up. There shouldn't be a need to run the pump for as long as you are, even at low speed. Remember, you are generating chlorine for a percentage of the time the pump runs. I would think that 2 hours on high and about 12 hours on low should be more than enough.

 

[peterl1365]

I'm sure you're right about having to bump the percentage up as the water gets warmer.

I was under the impression, however, that lower CYA levels promoted better FC effectiveness.

 

[chem geek]

It's not that lower CYA promotes more chlorine effectiveness unless you are comparing the same FC level. Yes, at a given FC level, the lower CYA has more disinfecting chlorine than a higher CYA, but the way to look at it is that you can get the same chlorine effectiveness at the higher CYA by having a higher FC.

So yes, normally you would want to run your pool with the lowest CYA possible to minimize daily chlorine losses (from sunlight, mostly) balancing needing less chlorine at lower CYA against CYA's protecion of chlorine from sunlight and for non-SWG pools this usually means a CYA level of 20-40 ppm. However, in an SWG pool, the SWG itself has an efficiency that we believe is a function of the CYA level. We've had quite a few pieces of evidence from users now where a higher CYA level makes the SWG cell more efficient at generating chlorine so that to maintain the same FC level the "on" time of the SWG cell can be cut way down. I believe that what is happening is that the higher CYA levels "take up" the chlorine that is generated in the SWG cell faster so that it appears as if there is less buildup of chlorine at the cell plates and that makes the generation of chlorine faster. I actually calculated all of this using rate constants and was shocked to find out that the math worked out almost precisely at typical flow rates such that a CYA level of around 50 or more allowed the CYA to take up the chlorine at a rate that was faster than the chlorine generation including the sweeping away of it through the cell from the water flow. The actual amount of CYA needed for this efficiency jump will likely be dependent on the specifics of the SWG cell -- the flow rate between the plates, the size of the cell, etc.

Think of it this way. Let's say that you have a room with doors going into it and a single door exiting it. There are people streaming into the room from the input doors (that's chlorine generation). They jam up, however, trying to get out of the single exit door (that's chlorine buildup in the SWG cell between the plates). This is what happens when there is too little CYA. The rate of production of chlorine is cut down by the fact that too much chlorine builds up at the plates. With higher CYA, this is as if you widen the exit door or add more exit doors so that the people can stream out of the room more quickly. This allows more people to enter the room which is analogous to more chlorine being generated at the plate. Technically, it's not that the chlorine is actually removed from the SWG cell any faster, but rather that it is "hidden" from the generation plate by being bound to CYA as new compounds. Essentially, the reverse reaction of chlorine hitting the plate is cut down by having it "stored" as a new Cl-CYA chemical.

 

[cliff_s]

I will agree to the lower the CYA level the faster the chlorine is absorbed by the UV of the sun.
The converse is the higher the CYA level reduces the effectiveness of the chlorine.

I am really sceptical on the chlorine take up theory. In my experience the high CYA levels are to cover up
for installing too small a SWG unit. It makes the test kit reading OK, but negates the chlorine effectiveness.
The same process happens when using Tri-Chlor tabs. The high CYA levels make the test kit read fine but
the chlorine is doing nothing. Some cover this up with so called shocking the pool. This raises the chlorine
levels to a point where the chlorine is effective.

The chemical levels that are used in Salt pools come from what is used for none salt pools. I haven't
seen any credible research on the difference in algae growth between the two systems. Also, on the levels
required for bacterial supression. The sodium addition to the water changes the environment in which the bacteria
thrive. Sodium will poison some types and encourage others. Until good scientific research is done by credible
labs, we are only guessing on the levels of chlorine, pH and etc. that we need to in our salt pools.

Cliff s

 

[Guest]

Cliff,
Salt pools have been in operation for over 30 years now! I think we have enough empirical evidence on the levels needed to properly maintain them. Most residential SWGs operate at well below maximum settings, do not develop algae, and have disinfected water. Also the great majority of SWG pools never need to be shocked (as determined by having any combined chloramine.) I base these last statements on my own pool, the pools of my customers, and the the results reported by owners of salt pools on this and the 4 other boards I am active on. I do not know where you are getting your information but it certainly goes against 30+ years of salt pool use.

Also, trichlor tabs can be used sucessfully to maintain proper chlorine and stabilizer levels in areas of the country with short swim seasons that winterize their pools and if the pools have sand or backwashing DE filters that are backwashed on a regular basis. Even here in Florida I have customers with sand and De filters and pools that are not too large that are able to maintain a good equalibrium between the amount of stabilizer added by trichlor and the amount removed by backwashing who do not run into problems with high stabilizer levels in trichlor sanitized pools.

 

[chem geek]

Some posts got lost from the previous forum so I'll copy some of those over here. First is the response from cliff_s to waterbear as follows:

Just because something has been around for years doesn't mean that the science has been done.

Only in recent years has ORP been included in pool measurements. Many of these issues come up
in large public pools that are regulated by the various departments. There is even an issue whether
the saturation index should be used and if it even applies to pools. When I go to the pool store it frightens
me when I read what is contained in the so called pool improvement products. None of these products are
meant for human consumption, yet they are poured into the pools we swim in and sometimes we accidently drink.

The real question that needs to be answered scientifically is what level of chlorine is effective in salt pools.
Since we a dealing with salt water and not fresh water the types of algae and other creatures that flourish are different.
Also, what is the effect on Guardia, E Coli and its friends. Water companies deal with these issues as a matter of course,
but they only deal with fresh water.

In Salt Pools we use electrolysis to liberate the chlorine from the salt(Sodium-chloride), but at the same time we also liberate
many other products, hydrogen, oxygen, sodium, calcium and various metals depending on the composition of the fill water.

What really needs to be done is a credible biology lab. to research this issue and publish the results. Then we can determine the
the proper parameters to efficiently operate our pools. Do we get added sanitation when the water passes through the cell ?
If so, how much. Do we really need 2 ppm+ of residual chlorine in a salt pool with 3000ppm of salt. How about the relationship
between Alkalinity and pH.

What is needed is good science and not salesmanship with so called facts off the top of ones head or we have always done it this way
so it must be right.

Cliff s

 

[chem geek]

Next is The Mermaid Queen's response:

I am not nearly knowledgeable enough to touch on the other parts of this comment, but I will say that a salted pool is not the same as 'salt-water'. Sea water has a salt content of about 35,000 ppm, whereas a 'saltwater pool' has about 3500, making the ocean 10 times saltier. Not to mention that there is not chlorine sanitizing (or killing) organisms in the sea. There is still chlorine at work in a 'saltwater pool', it is just from a different source.

ETA: if the people running salt pools do so at 'whatever rate' of chlorine production and they have no algae growth or combined chloramines, that means the chlorine rate is effective in doing its job.
That's all I will say, as I am headed toward the deep end and don't want to get totally over my head!!

 

[chem geek]

Next is waterbear's response:

I am glad you mentioned ORP measurements. ORP only works if there is NO CYA present. ORP readings go down very fast in the presence of CYA and there is also no true relationship between the oxidation potential of a chemical and it's sanitizing aiblity. Both Ozone and MPS (and such chemicals as sodium percarbonate, hydrogen peroxide, and even molecular oxygen ) will raise ORP readings and have higher redox potentials than hypochlorous acid but do no act as sanitizers while certain metal ions such as silver and copper do have bacteriostatic effects but no effect on ORP readings. Salt levels do not affect ORP, btw. Biguanide is an EPA aprroved sanitizer but it is not an oxidizer so it has no effect on ORP readings and they are useless in a biguanide sanitized pool except perhaps to check on peroxide levels but give no indication of the sanitizing ability of the water.

The products produced at the electrodes of a salt cell are chlorine gas and hydrogen gas. The other ions you mentioned such as sodium and calcium are in all pool, whether there is a salt generator or not. They comprise what we call TDS (along with other ions such as sulfates and magnesium). TDS in itself is not a problem but certain components of it can create problems such as sulfates or calcium when the levels get too high. The amount of chemicals that might accidently be ingested by drinking pool water is very tiny since the concentrations used in pools is very dilute. Drinking water has higher allowable levels for many of the things we put into pools. Perhaps if you are that afraid of what is in pools you might want to consider staying out of them.

 

[chem geek]

And last (so far) is my (chem geek's) response:

cliff_s,

Believe me, I'm completely with you on basing information on scientific facts, careful experiments and studies. However, I also believe that the science has to explain what goes on in real pools and if there's an inconsistency, then the science needs to be examined to explain what really goes on. As waterbear points out, there has been a lot of feedback from users of several pool forums and that is where the basis comes from regarding lower levels of Free Chlorine working well in most SWG pools.

If you haven't already seen my posts regarding the chemistry of pool water, take a look at this thread where I talk about (and calculate) the chlorine/CYA relationship. At the end of the first post is a link to a spreadsheet that calculates the pool water chemical species including the chlorine/CYA compounds (chlorinated isocyanurate species). At post #45 in this long thread I calculated the chlorine concentration buildup based on CYA concentration and assumed water flow through the salt cell. It may very well be the case that the SWG manufacturers have mostly simply decided on 60-80 ppm CYA just to protect chlorine a little bit longer (but not that much longer -- the half-life for chlorine in direct noontime sun is 6 hours at 30 ppm CYA and 7 hours at 60 ppm CYA so the returns are definitely diminishing). However, more and more users have been reporting that the higher CYA levels have lead to dramatic improvements in salt cell efficiency in that they can turn down their salt cell "on" time far below what would be explained by the breakdown of chlorine from sunlight at different CYA levels.

You can also look at this thread where I look at disinfection rates and show that a very, very small amount of disinfecting chlorine kills most bacteria and inactivates viruses (but protozoa such as Giardia and Cryptoporidium are very hard to kill using chlorine alone). The intermediate exception is the bacteria, Pseudomonas aeruginosa, that causes "hot tub itch" which requires higher levels of chlorine than we recommend for pools, but this bacteria seems to thrive much more in the hotter water found in hot tubs so that's where the higher disinfecting chlorine levels really need to be used. The issue with needing chlorine in pools is mostly to keep away algae since it takes higher levels of chlorine to kill algae than it does to kill the "easy-to-kill" bacteria. Ben's Best Guess CYA chart was created from his experience with many commercial pools plus residential pool users' experience on the Pool Forum. The chart's "Min" and "Max" columns very much track actual disinfecting chlorine levels of 0.03 and 0.07 ppm (of HOCl, measured as ppm Cl2) except for very low CYA levels where the minimum chlorine is more determined by not having it run out (i.e. it is hard to keep 0.1 ppm FC in the pool, not only due to sunlight, but due to localized consumption).

You are right about salt pools possibly influencing different species of algae, but remember that a regular pool starts out with about 350 ppm salt (chloride as ppm sodium chloride) due to the initial addition of sodium bicarbonate with calcium chloride. Over time with the addition of chlorine, this salt level rises to around 500-1000 ppm in most pools, especially those using a liquid form of chlorine (bleach or chlorinating liquid) which contains salt as well as hypochlorite. The level of salt in modern SWG pools is 3000 ppm which is not that high especially compared with the ocean at around 35,000 ppm. So though there is a difference, I doubt that the species of algae in 3000 ppm pools is significantly different than in non-salt (350-1000 ppm) pools, though only real testing can determine that for certain.

A vigorous discussion of the Langelier Saturation Index may be found at this thread. This thread shows a large study of commercial pools and is the main study the pool chemicals and distribution industry uses to claim that CYA levels do not matter (only Free Chlorine matters). And just to show that I am not biased towards salt pools, this thread talks about possible downsides to the extra salt and the SWG (I'm not biased against, either -- I just feel that full disclosure of information is useful to make wise decisions).

Over the past couple of years I believe that several of us on the Pool Forum have added some scientific backing and explanations to the experiences that pool users have been seeing. I absolutely agree that we have NOT done rigorous experiments, but unfortunately there have been very few such studies and some of those that have been done were done in ways to bias the data through incorrect methodologies (in my opinion) while others have not. In some cases we have tried to "experiment" using real pools and that's how we determined the amount of disinfecting chlorine needed to keep away mustard/yellow algae -- a couple of users actually varied their pool's chlorine levels to see the algae go away, then come back, by raising and lowering the chlorine level. There have also been "experiments" with many pools regarding the "rising pH" problem, especially in SWG pools and I would say that we have definitively determined that lowering the TA level reduces the rise in pH and especially the amount of acid needed to keep the pH stable. This is a strong indicator that our "theory" that the cause of the pH rise is due to the greater outgassing of carbon dioxide from the aeration from the hydrogen gas bubbles generated in the SWG is correct. If the conventional wisdom that the SWG produces alkalinity (from hydroxide) were the true cause, then lowering the TA would not have helped the problem -- it would have made it worse as far as pH rise and would have had no effect on the total amount of acid needed to maintain pH (this post describes how the use of bleach, chlorinating liquid, and an SWG are pH neutral in terms of chlorine addition AND usage combined). We also believe that the use of borates helps reduce the rising pH problem though we are less certain as to why (we think it's due to the borates inhibiting algae so that less chlorine is needed to do so) and more info on this can be found at this thread.

Anyway, if you have information on scientific studies or suggestions for experiments or anything else that can be helpful in our quest to understand what goes on in pools so that we can directly address problems and, most importantly, prevent them at low cost and with ease-of-use, please let us know. This has been a group effort and we encourage and appreciate all feedback.

Richard

 

[SeanB]

Bless you!

 

[peterl1365]

Thanks for all the great replies. I didn't mean to stir up such a heated discussion, but it's all been very useful.

I'm going to follow the advice of Evan and Richard. I'm slowly adding CYA and plan to bring it to the 50-60 ppm range.

My question, then, is what FC level should I shoot for? All the guidelines say 1-3 ppm, but it sounds like I want it to be somewhat higher. What level is considered safe for swimming? I was under the impression that we should not go in the pool until the FC level had dropped to under 5 ppm.

If my SWG generator efficiency goes up, and the FC is less likely to break down, then I should be able to maintain my desired (elevated) FC levels at even lower SWG runtimes than I currently use. This should also help counteract the constantly rising pH problem that I have. I'm currently adding about 4-8 oz of muriatic acid per day to keep pH levels under control.

Anything wrong with this logic?

 

[chem geek]

Definitely keep a minimum of 3 ppm FC. Most users with SWG systems even with a CYA of 70-80 ppm are able to keep clear pools with 3 ppm FC. Some SWG users got green algae when their FC was only at 1-2 ppm. The extra superchlorination in the cell helps to kill free-floating algae. That won't help algae stuck on surfaces, but with regular brushing 3 ppm FC should be fine. If it's not, you can always move up to 5-6 ppm FC which should be enough to keep away even mustard/yellow algae in an SWG pool.

Going into a pool with more than 5 ppm FC is perfectly fine if the CYA level is high. It's the disinfecting chlorine concentration that is the issue and it's lower at higher CYA levels. Don't forget that indoor pools with 2 ppm FC and no CYA have as much disinfecting chlorine as a pool with 20.5 ppm FC and 30 ppm CYA (believe it or not). This is why my wife's swimsuits degrade in less than one winter when using an indoor pool (with no CYA) compared to no degradation whatsoever during any summer in our outdoor pool that has CYA in it. The disinfecting chlorine determines the rate of killing algae, killing bacteria, fading/degrading swimsuits, oxidizing organics, etc. The FC level only tells you the total capacity (reserve) of chlorine. You can consider the chlorine "protected" by CYA to be in reserve and not active -- it just replenishes the disinfecting chlorine as it gets used up.

Yes, you should be able to lower your SWG runtime and that will help less the pH rise in your pool (due to less hydrogen gas bubbles so less aeration). If you don't already have your TA lowered to 80 or so, you should do that as well since that will also help lower the tendency of the pH to rise. In fact, I would get your TA lowered first before you muck around with the CYA. It's easy to adjust TA, but CYA is hard to lower if you decide to change your mind. What is your current TA level?

 

[peterl1365]

Richard,

I'm not completely certain about my TA level. I have an Aquachek Trutest meter which I use, and the TA readings vary between 70 and 130. A lot of the variance probably comes from me constantly adding muriatic acid. The meter is also a likely source of significant error.

I had the water tested at Leslies about 2 weeks ago. At the time, they measured it at 120 ppm. So, my "real" TA is probably between 100 and 140 ppm.

Your explanation of CYA is a good one. I guess it's almost like a chlorine buffer. Would that be a good analogy?

Thanks again Richard. You've been a great help. Once I nail down the TA measurements (I'll have to buy a good kit), I'll try reducing it gradually and then adding borates like Evan did. I'm just getting tired of having to check pH levels everyday. By the way, for pH measurements, I'm using an Omega Instruments pH/Conductivity meter which has a supposed accuracy of +/- .02 pH. It's actually interesting to see how the pH varies in different areas of the pool even before I add acid. It's not a whole lot, but it's in the range of .10 to .15 pH. I attribute the differences to the SWG cycling on and off.

edit: FWIW, I should add that this is a brand new pool that was just plastered on March 10, 2007.

 

[chem geek]

Yes, you can certainly consider CYA a "chlorine buffer". It not only stores a "reserve" of disinfecting chlorine (hypochlorous acid), but it does in fact buffer it against changes from other factors in a way not dissimilar to how the carbonate buffer keeps pH more stable. So with CYA in the pool, the disinfecting chlorine concentration doesn't vary as much with pH as it does when there is no CYA in the pool. You can see this in the graphs in this post.

 

[cliff_s]

Now, for a couple of practical comments. I do use CO2 for pH control and with a 20,000 gal pool, a 20 lb bottle will last about 6 to 8 weeks in the summer and 3+ months in the winter.
When I first tried the CO2 I was amazed at how fast it brought down the pH. Of course it does nothing to control the TA, so I have to use acid also. I did find in a previous pool in
which I used a peristaltic pump to add the acid, that adding a little acid everyday really did a better job of controlling the parameters. With just adding acid alone it is impossible to have
the proper TA and pH at the same time. To keep the pH down(offset the the raising of the pH by the salt cell), if you use just acid alone you will find that the TA will also continue below the desired level.

There is all sorts of speculations of what happens when the water is passed through the salt cell it self. First: current is passed through the water which will affect whatever is living in the water.
Second: Chlorine is liberated from the dissolved salt. This will kill living organisms. Since in order for current to pass through the water the water must be somewhat conductive(lowered in resistance)
so the voltage is within reason for current to flow. We have done this by addition of salt which contains Sodium which is a conductive metal. Now at the current density that is used in a salt cell
what effect does current have on living organisms. Since the chlorine literally bubbles off the plates the chlorine density within the cell must be greatly increased. We know that the higher the density
of the chlorine the faster the kill of organisms. Another factor is the internal heating cause by the resistance of the water and the current through the cell. How does the velocity of the water affect
the sanitation within the cell itself.

Now, we pass most of the water in our pool through the cell and we know that something is happening to the water and its occupants both organic and inorganic.

Research needs to be done on just how much real sanitation is occurring in the cell and
does bacterial kill really occur. What type of bacteria is killed and the affect on the various types of algae. We know that sodium itself is a poison to some types of algae,
but I have not seen a studies as to the level of salt verses the growth of the various types of algae. I have read a couple of papers on Ozone cells, but that is little different
in that most Ozone systems are used for water purification and the Ozone is in contact with the water because the water itself is under constant pressure until used.
This is not the case in pools, so the Ozone just dissipates.

Another is the electroplating of metals. From observation one could certainly plate out the
calcium in the water. We know we can plate out the Sodium, because Sodium itself is very unstable it will recombine with whatever is close.

As far as the saturation index, with out going into a long diatribe, as long as we stay in the negative numbers(corrosive) we will keep the calcium in solution.
Since pools are designed to use chlorine which is extremely corrosive none of the mechanical parts will be made of corrosive materials. The saturation index
was derived for warm water boilers that use steel tubes and needless to say are very sensitive to corrosion. Is the index useful for pools, yes, somewhat.

The real question is are we spending our money, time and effort on the most efficient way of operating our pools. Having a engineering background I have always looked
for a better way of doing things. Questions I have asked are, if your water company which must be inspected by governmental agencies and have their product continually
tested keeps wider standards than is expected from pool owners, why are we trying to keep these standards and are they really necessary. Our pool stores would love to sell
us an armload of chemicals each time we come in(because it makes them profit), but is it necessary for the operation of our pools. This is where science comes in,
with laboratory research we find what is needed and what is not.

Cliff s