Why high CYA is a good thing with a SWG

[donaldm823]

I know it's a bit late since you removed the SWG but I know why you had so many problems with it if your last water test is typical. Your stabilizer level is 30 ppm and that alone is enough to cause early cell failure and major pH problems leading to scaling and short cell life! This is why Goldline recommends a CYA of between 60-80 ppm. It's in your user's manual (you DID read the manual, right). If you would like a detailed explanation of why having too low a CYA level can cause cell failure and pH and scaling problems I would be happy to provide it but it is technical. What I am surprised at is that your local Pinch a Penny did not catch this! (Actually, I'm not that surprised. I work in the industry. )


Hope this is helpful.

I would appreciate the detailed tech explanation why running a SWG at a low CYA level (30ppm range) is harmful to the SWG cell. If too involved for this forum post could you send me a private message? Thanks much-I tried to send you a private message but may not have been successful

 

[SeanB]

Your message will stay in your outbox until the sender opens the message on their end. Until it has been opened by the recipient, you can still edit or delete the message.

 

[Guest]

PM answered!

 

[JasonLion]

I split this off from the original topic because I think that it is an interesting question that deserves to have an answer others can see on the forum. In general when asking a question it is best to start a new topic so the answer can be shared with others and not get mixed up with posts on an existing topic.

Despite what a great deal of the available literature says, higher CYA levels reduce the total amount of chlorine required to sanitize your pool. Even though a higher CYA level requires a higher FC level, the amount of chlorine you need to add each day to maintain that higher FC level is actually lower than what you would need at a lower CYA and FC level. This happens because CYA protects FC from sunlight, reducing the amount lost to sunlight enough to more than make up for the higher FC levels required.

Since less total chlorine is required at higher CYA levels, the SWG cell doesn't need to run as long each day. Since the cell in a SWG has a lifetime based primarily on how long it is on, a lower daily run time results in longer cell life.

 

[JasonLion]

waterbear-got your PM on SWG pool chemistry.

It is a superb chemistry intro that is worthy of posting to all. It gave me some insights that I was not aware of and more importantly, it has adjusted my thoughts on how best to maintain my pool chemistry. Thanks again

 

[waste]

PM answered!

Evan, care to share what you answered? You know this is something I'm interested in - could you please post what you said?

 

[donaldm823]

I split this off from the original topic because I think that it is an interesting question that deserves to have an answer others can see on the forum. In general when asking a question it is best to start a new topic so the answer can be shared with others and not get mixed up with posts on an existing topic.

Despite what a great deal of the available literature says, higher CYA levels reduce the total amount of chlorine required to sanitize your pool. Even though a higher CYA level requires a higher FC level, the amount of chlorine you need to add each day to maintain that higher FC level is actually lower than what you would need at a lower CYA and FC level. This happens because CYA protects FC from sunlight, reducing the amount lost to sunlight enough to more than make up for the higher FC levels required.

Since less total chlorine is required at higher CYA levels, the SWG cell doesn't need to run as long each day. Since the cell in a SWG has a lifetime based primarily on how long it is on, a lower daily run time results in longer cell life.

Waterbear also had some insights as to pool chemistry parameters in regards to a pool with a SWG. These revised parameters go hand in hand with the same ideas of higher CYA when using a SWG for chlorine control. Waterbear recommended different pH and TA concentrations, so I suggested a posting of the entire PM as it was a great summary. I guess I could paste the email in here-but it would be better if waterbear would post the entire PM that was sent to me since waterbear is the author. Sean-let me know

 

[DONNIE]

Me Too

I too would love to see it. I just finished my first year with my new pool and had a "troublefree" year. Not one water problem thanks to all the education I got here prior to the first fill.

Donnie

 

[mas985]

I did a series of tests over the summer on both my pool and spa. The tests are summarized here:

http://troublefreepools.com/viewtopic.php?t=3184

and here

http://www.troublefreepool.com/viewtopi ... =4482#4482

The bottom line of the testing was that the cell produced the same amount of chlorine no matter what the CYA level was and it was very close to what the maufacture specified as the production level.

However, the extinction of chlorine reduced significantly with higher CYA levels. So even though you have to run at higher chlorine levels with higher CYA, you actually lose less chlorine per day at higher CYA levels.

I try to maintain a CL level of 5% of my CYA level. So to give you an idea of what CYA does, here is a summary of some of the testing I did.

CYA = 45 ppm, CL target = 2.25 ppm, CL extinction/day = 1 ppm, SWG setting 60% for 6 hours
CYA = 80 ppm, CL target = 4.0 ppm, CL extinction/day = 0.5 ppm, SWG setting 35% for 6 hours

So even though I needed almost twice the chlorine level at CYA of 80 ppm, I could get by with almost half the chlorine production.

I surmise that higher CYA levels may also be beneficial to BBB users as well since it really does not depend on how the chlorine is introduced into the pool. It seems you will always save money on chlorine or cell life with a higher CYA.

There are downsides to higher CYA such as plaster erosion, chlorine measurement and fighting algae if a bloom occurs so most suggest 80 ppm as an upper limit.

 

[Guest]

Ok, here is the original PM (including a quote from my original post at the end in bold)and my answer:

donaldm823 wrote:
Dear waterbear:
I read the following post from you saying you could explain why CYA must be in the 60ppm range for a SWG or cell failure would result. I just installed a Autopilot Digital and left my CYA at 30ppm since I only had a month left in my pool season. Since it ran so well in Sep , I was considering leaving CYA at 30ppm for my next pool season vice raising it to 60ppm so that I could keep my FC lower, use less Chlorox when shocking, and keep the algae at bay!.

Could you email with the tech explanation why I need the 60ppm CYA level? I thought the 60ppm was just so the SWG cell could run less time and give the chlorine a chance to mix with the pool before it was impacted by the sun. But your email (I quote below), implies something more sinister and alerted me that maybe I should be following the owners manual and accept a higher FC level. I have the SWG-60 which is rated for a 60,000gal pool (mine is 30,000). I also watch chemistry closely on a daily basis with my LaMotte ColorQ, so I keep pH in check.

Don

I know it's a bit late since you removed the SWG but I know why you had so many problems with it if your last water test is typical. Your stabilizer level is 30 ppm and that alone is enough to cause early cell failure and major pH problems leading to scaling and short cell life! This is why Goldline recommends a CYA of between 60-80 ppm. It's in your user's manual (you DID read the manual, right). If you would like a detailed explanation of why having too low a CYA level can cause cell failure and pH and scaling problems I would be happy to provide it but it is technical. What I am surprised at is that your local Pinch a Penny did not catch this! (Actually, I'm not that surprised. I work in the industry. )

Here is my answer to the PM:

Nothing sinister but just some basic science and water chemistry and an understanding of how a SWG works and interacts with the water chemistry. Having CYA in the recommened range allows the cell to maintain the FC at the desired level with a lower output percentage than if the CYA is too low. This has several ramifications.

The first and most obvious is that a lower output percentage directly translates into a longer cell life! (This is also an excellent reason NOT to use the boost or shock feature of a SWG but to shock with liquid chlorine instead but is not actually the BEST reason to do so. Without getting into the chemistry involved let's just say that using liquid chlorine and adding the full amount needed all at once is going to produce more efficient shocking than the gradual increase over a 24 hour period of FC by using the boost or shock function.) Cells are rated in hours of life and the less time it spends in the on state the longer it will last!

The second reason is also linked to output percentage. When the cell is generating chlorine it produces clorine gas at one electrode which dissolves in the water to form your active sanitizer, hypochlorous acid. Exactly the same as if you had added liquid chlorine. However, the other electrode is producing hydrogen gas bubbles. These aerate the water, which causes carbon dixoide to outgas (Your pool is overcarbonated, we call this Total Alkalinity!) The outgassing of carbon dixoide causes the pH to rise! (Carbon dioxide in water is basically, for our purposes here, carbonic acid -- think seltzer!--Shake it up and the carbon dioxide bubbles off and the seltzer turns to water--the carbonic acid disappears!) pH rise is a major problem with salt water genterators so by maintaining the proper CYA level in the water you can help minimize this pH rise and help reduce your acid consumption.

pH rise can be responisble to shortened cell life because pH rise is the ONE FACTOR that will predict scaling condition. High pH leads to scaling, period! ( I will not go through a lengthy explanation of the Langelier Saturation Index here but I have discussed this at length before at Poolforum. com. )
Scaling can shorten cell life if allowed to build up. Cleaning cells on a regular basis is a pain. Runing the proper CYA level helps slow scaling by allowing for a slower pH rise.

All these factors will contribute to a longer cell life and they are all accopmplised by running the CYA at the recommened level!

Now for a few more things to think about. The manuals for just about every SWG on the market recommend a FC between 1-3 ppm. Actual practice indicates that a FC between 3-5 ppm makes the pool virtually trouble free in regards to needed shocking because of CC or in reguard to algae breakouts. This is still lower than the recommened FC level for a manually chlorinated pool with the same 60-80 ppm CYA! No one is able to really explan this but it is suspected that is is caused by the constant 'supershocking' of the pool water as it flows thorough the cell in it's on state.

Running your TA on the low side will increase your pH stability and decrease your acid consumption. Like I said earlier your pool is carbonated. By lowering the carbonation a bit you lower the tendency for CO2 to gas off. Running the TA between ab out 70-90 ppm is a good range for a SWG (or ANY unstabilized chlorine source). The reason the higher TA readings have been so entrenched is because of the widespread use of trichlor and dichlor, both stabilized chlorine sources and both acidic! Having a high TA will cause more outgassing of CO2 and create a tendency for the pH to alway be rising toward aobut 8.2. This nicely offsets the acidic efficts of the trichlor or dichlor and helps maintain a stable pH. This is also why addition of baking soda to increase TA is a regular occuracne with stabilized chlorine and the use of muriatic acid is much less frequent but the opposite is true with unstabilized chlorine (including SWGs) where the use of muriatic acid to lower pH is the norm and very rarely does TA need to be increased (and when it is it is usually increased too much, leading to even worse pH instaiblity and scaling conditions since the pH now alway s wants to rise toward 8.2 until enough of the TA has been destroyed by the additon of acid to get the pH in line!)

Also, running your pH at 7.6 and NOT LOWER will slow the outgassing of CO2. The lower you place the pH the faster outgassing occurs. This is why we purposely drop the pH low when we want to lower TA! My rule of thumb is to keep the pH at 7.6 and when it hits 7.8 it's time to add enough acid to lower it back down to 7.6. A bit of trial and error will soon teach you how often and how much is needed!

Adding borates to your water in a 50 ppm concentration will help with pH stablilty with a SWG, particularly when the TA is run in the 70-90 ppm range jand pH is kept between 7.5-7.9 (a little wider window than without the borates!). There are several reasons why:
It introduces a secondary borate/boric acid buffer into the water which works in the oppsite direction of the carbonic acid/carbonate/bicarbonate buffer we call TA. Instead of moving the pH up it moves the pH down. This effectivly tends to 'lock' the pH around 7.6 to 7.7 for a long period of time compared to without the borates.

It has algaestatic properites so instead of relying on the chlorine to kill nascent algae blooms which are always occuring these are kept at bay. This allows you to run the cell at a lower output since it lessens the chlorine demand (sometimes by quite a lot!) Running the cell at a lower output causes less outgassing of CO2, etc., etc.


Finally, a few things about your ColorQ. Don't trust the CH test if your calcium levels by a titration test are within 100 ppm of the upper limit of the ColorQ (which means if your calcium when titrated is above 300 ppm!) This is a known problem with all of LaMottes colorimetric based CH tests that they do not like to disclose. I use LaMotte water testing at work and only after presenting them with repeated documentation of discrepencies between the results I obtained with their Waterlink Express and with EDTA based titrations for calcium hardness when calcium levels were high did they admit that the calcium test can become very inaccurate and read low when the calcium range is either higher than the meter's range or withing 100 ppm of the upper limit of the range! You should have no problems with the other tests in the kit but be aware that some of the precision ranges are greater than for the same tests done with a Taylor kit (CYA, TA, CH). This, once again is because of LaMottes colorimetric tests vs. a drop based titration test. (I'm talking about the TA test here).
The Chlorine and pH tests are going to be extremely accurate but be aware that the chlorine test is a DPD test so it is susecptible to bleach out when the chlorine levels are aboeve 10 ppm, leading you to believe that there is no chlorine in the water when the chlorine levels are actually high. This is not just a LaMotte problem but is common to all DPD chlorine tests (But NOT FAS-DPD titrationt tests for chlorine, nor OTO (yellow) tests for TC)
Also, be aware that pH should NEVER be tested when FC is above about 8-10 ppm because it will read high. Once again, not a LaMotte problem but just an interference between the phenol red indicator used to test pH in pools and levels of sanitizer.
Hope this is helpful.

P.S. I just want to add that I have a large customer base and have had many people come in with problems with their salt pools ranging from black algae and mustard algae! to just not being able to maintain any chlorine and by insuring that the CYA was within range (In EVERY case it was too low!) and maintaining proper pH (Many of them had pH readings of 8.0 and above) the problems were effectively solved (with what ever other treatments might have been needed such as maintaining high FC to kill algae, etc) and have not reoccurred. That alone has been enough to convice me that running the recommened CYA levels for a SWG is the right thing to do even if I did not understand the chemistry behind it!

 

[chem geek]

An outstanding writeup! Should probably be a sticky on CYA and SWG though it also contains good info about having a lower TA to reduce pH rise which can occur even in non-SWG pools (this thread gives an extreme example where a TA of 50 in a couple of non-SWG pools was the "sweet spot" though their CYA level was lower so was equivalent to 60-65 for an SWG pool with higher CYA). This chart quantifies the principles of how a higher TA and lower pH outgas more rapidly. The chart was for a CYA of 30, so with a CYA of 60-80 the numbers in the Total Alk. column would be increased by around 10-15 though this is really pH dependent. The principle remains the same, however -- to reduce the rate of pH rise, lower the TA and maintain a higher pH target. Since the chart only gives relative rates since it's dependent on aeration, wind and other factors, it isn't a single "answer" for any pool.

Richard

 

[waste]

Evan and Mark, thank you for the replies :!: You may recall a rant I started last year at PF on this subject. What you've said here answers that issue (if someone from Goldline had been able to tell me this, the rant would have been confined to ProTeam - though I've revised most of my opinions on the products I use).

It seems to me, from what you both are saying, is that every pool should have a cya of 60 - 80 regardless as to whether it has a SWCG or not. IF I'm reading this correctly, the higher cya will cause a higher initial dose of cl, but protect the fc much better and actually cause a lower demand for 'fresh' cl. daily. Is this something we should all practice, regardless as to our cl source? (and the borates)

Thanks for the info, I'll try to remember to write up a Rx for my boss's customers over the winter.

 

[JasonLion]

There are disadvantages to high CYA, for example far more chlorine is required to shock the pool. So it isn't obvious that this reasoning applies to all pools. With a SWG the disadvantages of high CYA are minor compared to the advantages. But when using liquid chlorine/bleach it is far less clear. When using dichlor or trichlor you want to keep CYA as low as possible, since it will get high no mater what you do. Similarly, the PH and TA reasoning is based on the constant aeration from the SWG. In pools without a frequent/constant source of aeration, and in pools using dichlor/trichlor regardless of aeration, other factors come into play and the ideal levels will be different.

 

[Guest]

I will rewrite the info I posted as a sticky on water balance "tweaking" for SWGs as soon as I get a bit of free time. (And I will get rid of the typos too! )

It really isnt' rocket science once you understand what is actually happening in your pool! Just common sense. I have to give a LOT of credit to chemgeek for the info. He provided quite a bit of it. I just put it together and tried it out on my pool and my cusotmer's and found that it works! (Theoretically it made perfect sense but to find out that it works in a real world environment was a pleasent surprise! Just because something should work theorectically doesn't mean it will work once you test it! Remember that theoretically phosphate removers make good sense but they just are not really needed in MOST (I said most and not all!) real world applications! )

 

[mas985]

Jason makes a good point. I would not recommend adding CYA to pools using trichlor or dichlor pucks but CYA tends to be high anyway for those pools.

For BBB pools, it could be beneficial but it depends on the dosing method. Between large gaps in dosing, the CL level can get low and then the pool can be subject to algae blooms. If the dosing is quite often and regular then I can't think of any downside except for the shock level. However, even though the shock level is much higher, because of the retention benefits and the fact that CL levels will remain more constant between dosings (i.e. less absolute chlorine loss during the day), I bet you end up shocking less with higher CYA. Unless of course it gets too high but even then as long as you keep the CL level at 7.5% of the CYA level per Chemgeeks chart, there should not be an issue.

For pools that use the liquidator, there should not be too much difference than a SWG pool other than the PH creep. Both introduce CL at a regular rates so I would think CYA of 60-80 could be beneficial there as well.

So the only downsides of higher CYA that I know of are:

Shock Levels - which can be avoided with proper water chemistry and near constant CL levels
Plaster Erosion - which can be avoided by keep the CYA below 80 ppm
Chlorine Testing - which can be done with a FAS DPD kit or even a DPD kit for SWG pools

 

[chem geek]

I agree with what you are saying, but there's also a psychological factor and a practical matter. At 60-80 ppm CYA in a manually dosed pool, the minimum FC is around 4.4-5.8 ppm and for some people this "seems" like a lot of chlorine so they may let it drop below this level. For safety, the target level of 7-9 also seems really high. So if people let the FC drop to 3 or 2 ppm at the higher CYA and the water starts to get dull and then cloudy, it then takes a LOT of chlorine to combat the pending bloom, especially in larger pools. To do so quickly would take 24-31 ppm FC but in practice and in the spirit of Ben's original table a level of around 20 ppm FC would work OK. The usual advice is to do a partial drain/refill to lower the CYA so that less chlorine needs to be used to battle the algae, most especially if the algae is of the mustard/yellow variety.

At these higher FC levels you'll have pool stores, PBs and others jumping up and down swearing that you are overdosing your pool with chlorine and that it's dangerous and it's outside the NSPI ranges, etc. What they say is not true (about it being dangerous), but you'll get a lot of flak.

So I agree that if you use The Liquidator or are otherwise diligent about chlorine addition, then there should be no problem. I just see so many people letting their pools go even by accident and then when they need to get rid of the algae, it's much harder to do at the higher CYA levels without using lots of chlorine or some, gulp, copper algaecide or phosphate remover (these aren't needed, but they are quick for resolving the algae problem, and then causing others...).

Now, all that said, I'll probably be raising my own CYA level a bit more this next season. I have an opaque electric safety cover so the chlorine loss from sunlight is low so I don't need much higher CYA levels for that reason, but I do now get a loss of around 1 ppm FC per day since my wife's been using the pool more frequently so having a higher CYA level would let me add chlorine twice a week (every 3-4 days) as I currently do without having as large a swing in disinfecting chlorine concentration (i.e. 2.2-6.2 ppm FC at 30 ppm CYA is a broader disinfecting chlorine range than 4.5-8.5 ppm FC at 60 ppm CYA). When the chlorine daily loss was 0.5 ppm FC, a low CYA level was fine, but now I see another advantage to the higher CYA level (a sort of "mathematical ratio buffering" since it relates to (FC + incrFC)/CYA ).

Richard

 

[cliff_s]

CYA is only used to retard the dissipation of Chlorine by UV light from the sun. It is never used in a
indoor pool or a pool that is covered from the sun.

In the winter very little CYA is needed because of the shorter days that reduces the time the sun
has to eat your Chlorine. The only problem is that once you put CYA into your pool without draining
the water there is no way to get it out. This only leaves the option to run the level of CYA that is needed
in the middle of the summer when the sun is up the longest.

If you run your SWG during the night as most do to get the lowest rate on electricity, the Chlorine level
needs to last the entire time of daylight.

To determine the level you need, start with a lower level of CYA(30 ppm). Measure our Chlorine in the morning
after your SWG has shut off, then measure it again at dusk. This will give you how much Chlorine is getting
used during the day. As you add CYA you will notice that the Chlorine level last longer when the sun is out.
Keep adding CYA(10 ppm at a time) until you get the level you want at the end of the day. If you start out a 3ppm
in the morning your should have at least 2 ppm at dusk to maintain your Chlorine level.

You will hear many service people insist the you have 100 ppm+ of CYA for a SWG, this is pure bunk. What they
are doing to to cover up for installing a unit that is too small for your pool. Your SWG should generate enough Chlorine
during the hottest part of the summer by running no more than 8 hours per day. This will give some reserve for heavy
summer pool usage. The size of the unit is determined by the volume of your pool. The manufacturers rate their units
at 24 hour running time. Many claim that this is enough for your pool, but as most have found out this is just not true.
The ratings are also theoretical and derived form the current through the cell in an ideal condition.

Sure a smaller unit will work when the water is colder and the days are shorter and the sun is not out, but that is
not when you like to use your pool.

Actually you can time the running of your SWG with the length of the days and the temperature of the water.
This will give you constant Chlorine levels.

Cliff s

 

[chem geek]

CYA is only used to retard the dissipation of Chlorine by UV light from the sun. It is never used in a
indoor pool or a pool that is covered from the sun.

Cliff,

This is the conventional wisdom, but it does not take into account the fact that CYA doesn't JUST protect chlorine from breakdown from sunlight (UV rays), but also combines with chlorine to make the effective disinfecting chlorine (hypochlorous
acid) concentration FAR lower. See this post where you can see the traditional industry graph of hypochlorous acid (HOCl) and hypochlorite ion (OCl^-) vs. pH, but realize that this is only a correct graph when there is NO CYA present. I then show the correct graph with 30 ppm CYA where you can see that 97% of the measured Free Chlorine (FC) is chlorine combined with CYA (called chlorinated cyanurates) that are not effective sanitizers nor oxidizers. 1.5% is hypochlorite ion and 1.5% is hypochlorous acid (at a pH near 7.5) and only this latter 1.5% is an effective sanitizer and strong oxidizer.

This means that indoor pools that typically run at 1-2 ppm FC with no CYA are way, way, way over-chlorinated. There is plenty of confirmation of that as my wife and friends we've talked to around the country who use indoor pools that don't have CYA in them report swimsuit degradation (mostly elasticity loss, but also some fading even with fade-resistant swimsuits) over just one winter season of use (as well as greater skin flake/dry and hair frizziness). In outdoor pools with CYA, there is minimal such degradation even after 4 years. Furthermore, the very rapid and serious corrosion issues we have seen on pool forums with stainless steel in SWG pools have occurred with indoor pools with no CYA and not with pools with CYA (also see this PDF file that reports how CYA protected stainless steel in a high salt test).

The recommended FC/CYA ratio for manually dosed pools is around 11.5% and this results in a disinfecting chlorine (hypochlorous acid) concentration of 0.05 ppm and is technically equivalent to a pool (at pH 7.5) with 0.1 ppm FC and no CYA. If an indoor pool could maintain a 0.1 ppm FC consistently, then that would be fine, but with typical bather loads this is not possible as the chlorine gets used up locally so one has to have a higher FC to make up for localized demand. This leads to over-chlorination since the FC is raised to try and have enough chlorine to not run out (it's also difficult to accurately manage such a low chlorine level).

A solution to this problem would be to use CYA in indoor pools (and in pools with an opaque cover or that aren't exposed to sunlight) as the CYA isn't just to protect chlorine from sunlight, but also acts as a disinfecting chlorine buffer, keeping most of the FC in reserve and releasing it as needed. The disinfecting chlorine concentration is kept low, via the CYA, and that slows down all the chlorine reactions of disinfection and oxidation, but are still plenty fast enough to kill pathogens and prevent algae growth (as proven in outdoor pools with CYA).

Another positive side effect is that the lower disinfecting chlorine level produces a lower level of disinfection byproducts, such as nitrogen trichloride, and it's roughly proportional to the disinfecting chlorine level. With the latest breakpoint chlorination model I just got today (thank you for the reference, Dr. Valentine), 1 ppm FC with no CYA plus 0.05 ppm Nitrogen amount of ammonia (equivalent to 0.25 ppm Combined Chlorine after combining with chlorine) results in a peak of 25 ppb of Nitrogen trichloride (the chemical that smells the most, is most volatile, and is indicated in asthma, respiratory illness, occular irritation and a possible carcinogen) after 43% breakpoint completion in 9 minutes. If one instead has 4 ppm FC with 20 ppm CYA, then after around 30% breakpoint completion in 23 minutes there is a peak of Nitrogen trichloride of 7.4 ppb or less than one-third.

At the other extreme, having too much CYA without a corresponding increase in FC not only leads to low disinfection with algae (or dull cloudy water) being the most visible initial result, but it also leads to a breakpoint reaction that is too slow. At 3.5 ppm FC with 30 ppm CYA, the breakpoint is half complete after around 80 minutes and is 90% complete after 4 hours. With 2 ppm FC and 100 ppm CYA, the breakpoint is half complete after more than 6 hours and almost 20 hours to get to 90% completion. So monochloramine sticks around too long and can smell and be irritating (though not as much as Nitrogen trichloride).

Richard

 

[Guest]

CYA is only used to retard the dissipation of Chlorine by UV light from the sun. It is never used in a
indoor pool or a pool that is covered from the sun.

And an indoor pool will NOT have the chlorine loss of an outdoor pool, either

In the winter very little CYA is needed because of the shorter days that reduces the time the sun
has to eat your Chlorine. The only problem is that once you put CYA into your pool without draining
the water there is no way to get it out. This only leaves the option to run the level of CYA that is needed
in the middle of the summer when the sun is up the longest.

This is not really a problem. As the temperature drops just reduce the genterator output and reduce the pump run time. Once the temp drops enough the generator will stop producing chlorine anyway.

If you run your SWG during the night as most do to get the lowest rate on electricity, the Chlorine level
needs to last the entire time of daylight.

Which is why it's really best to generate the chlorine during the peak demand time, which will be during the day!

To determine the level you need, start with a lower level of CYA(30 ppm). Measure our Chlorine in the morning
after your SWG has shut off, then measure it again at dusk. This will give you how much Chlorine is getting
used during the day. As you add CYA you will notice that the Chlorine level last longer when the sun is out.
Keep adding CYA(10 ppm at a time) until you get the level you want at the end of the day. If you start out a 3ppm
in the morning your should have at least 2 ppm at dusk to maintain your Chlorine level.

You are missing the point that having the higher CYA will allow you to run the cell at a lower output to maintain the same FC level and this will, in turn, lead to better pH stability because of less production of hydrogen gas in the cell so there is less outgassing of CO2. It really has nothing to do with having a cell that is too small for the pool. Some manufature's units are marginal at best, and some of the ones combined with ozone or metal systems are definitely undersized but the majority of units are accurately sized.

You will hear many service people insist the you have 100 ppm+ of CYA for a SWG, this is pure bunk.

I have never seen a SWG that needed over 100 ppm CYA. Some manufacturers do recommend up to 100 ppm CYA with their unitis but if you look at the chlorine production of these cellss they are the marginal ones I spoke of above.

What they
are doing to to cover up for installing a unit that is too small for your pool. Your SWG should generate enough Chlorine
during the hottest part of the summer by running no more than 8 hours per day. This will give some reserve for heavy
summer pool usage. The size of the unit is determined by the volume of your pool. The manufacturers rate their units
at 24 hour running time. Many claim that this is enough for your pool, but as most have found out this is just not true.
The ratings are also theoretical and derived form the current through the cell in an ideal condition.

Sure a smaller unit will work when the water is colder and the days are shorter and the sun is not out, but that is
not when you like to use your pool.

Actually you can time the running of your SWG with the length of the days and the temperature of the water.
This will give you constant Chlorine levels.

Cliff s

The point is that the CYA is not necessarily to make sure there is enough chlorine in the water, but more importantly, to provide better pH stability and therefore less tendency toward scaling conditions. (High pH is the most important factor in predicting scaling condition,) It also helps prevent early cell failure by allowing the cell to be in the off state for a longer period of time each run cycle and by minimizing scale deposits in the cell. It also conserves electrictiy since the cell is in the off state for a longer percentage of each run cycle.

Sometimes one has to look at the bigger picture.

 

[dsilchenstedt]

Ok, here is the original PM (including a quote from my original post at the end in bold)and my answer:

donaldm823 wrote:
Dear waterbear:
I read the following post from you saying you could explain why CYA must be in the 60ppm range for a SWG or cell failure would result. I just installed a Autopilot Digital and left my CYA at 30ppm since I only had a month left in my pool season. Since it ran so well in Sep , I was considering leaving CYA at 30ppm for my next pool season vice raising it to 60ppm so that I could keep my FC lower, use less Chlorox when shocking, and keep the algae at bay!.

Could you email with the tech explanation why I need the 60ppm CYA level? I thought the 60ppm was just so the SWG cell could run less time and give the chlorine a chance to mix with the pool before it was impacted by the sun. But your email (I quote below), implies something more sinister and alerted me that maybe I should be following the owners manual and accept a higher FC level. I have the SWG-60 which is rated for a 60,000gal pool (mine is 30,000). I also watch chemistry closely on a daily basis with my LaMotte ColorQ, so I keep pH in check.

Don

I know it's a bit late since you removed the SWG but I know why you had so many problems with it if your last water test is typical. Your stabilizer level is 30 ppm and that alone is enough to cause early cell failure and major pH problems leading to scaling and short cell life! This is why Goldline recommends a CYA of between 60-80 ppm. It's in your user's manual (you DID read the manual, right). If you would like a detailed explanation of why having too low a CYA level can cause cell failure and pH and scaling problems I would be happy to provide it but it is technical. What I am surprised at is that your local Pinch a Penny did not catch this! (Actually, I'm not that surprised. I work in the industry. )

Here is my answer to the PM:

Nothing sinister but just some basic science and water chemistry and an understanding of how a SWG works and interacts with the water chemistry. Having CYA in the recommened range allows the cell to maintain the FC at the desired level with a lower output percentage than if the CYA is too low. This has several ramifications.

The first and most obvious is that a lower output percentage directly translates into a longer cell life! (This is also an excellent reason NOT to use the boost or shock feature of a SWG but to shock with liquid chlorine instead but is not actually the BEST reason to do so. Without getting into the chemistry involved let's just say that using liquid chlorine and adding the full amount needed all at once is going to produce more efficient shocking than the gradual increase over a 24 hour period of FC by using the boost or shock function.) Cells are rated in hours of life and the less time it spends in the on state the longer it will last!

The second reason is also linked to output percentage. When the cell is generating chlorine it produces clorine gas at one electrode which dissolves in the water to form your active sanitizer, hypochlorous acid. Exactly the same as if you had added liquid chlorine. However, the other electrode is producing hydrogen gas bubbles. These aerate the water, which causes carbon dixoide to outgas (Your pool is overcarbonated, we call this Total Alkalinity!) The outgassing of carbon dixoide causes the pH to rise! (Carbon dioxide in water is basically, for our purposes here, carbonic acid -- think seltzer!--Shake it up and the carbon dioxide bubbles off and the seltzer turns to water--the carbonic acid disappears!) pH rise is a major problem with salt water genterators so by maintaining the proper CYA level in the water you can help minimize this pH rise and help reduce your acid consumption.

pH rise can be responisble to shortened cell life because pH rise is the ONE FACTOR that will predict scaling condition. High pH leads to scaling, period! ( I will not go through a lengthy explanation of the Langelier Saturation Index here but I have discussed this at length before at Poolforum. com. )
Scaling can shorten cell life if allowed to build up. Cleaning cells on a regular basis is a pain. Runing the proper CYA level helps slow scaling by allowing for a slower pH rise.

All these factors will contribute to a longer cell life and they are all accopmplised by running the CYA at the recommened level!

Now for a few more things to think about. The manuals for just about every SWG on the market recommend a FC between 1-3 ppm. Actual practice indicates that a FC between 3-5 ppm makes the pool virtually trouble free in regards to needed shocking because of CC or in reguard to algae breakouts. This is still lower than the recommened FC level for a manually chlorinated pool with the same 60-80 ppm CYA! No one is able to really explan this but it is suspected that is is caused by the constant 'supershocking' of the pool water as it flows thorough the cell in it's on state.

Running your TA on the low side will increase your pH stability and decrease your acid consumption. Like I said earlier your pool is carbonated. By lowering the carbonation a bit you lower the tendency for CO2 to gas off. Running the TA between ab out 70-90 ppm is a good range for a SWG (or ANY unstabilized chlorine source). The reason the higher TA readings have been so entrenched is because of the widespread use of trichlor and dichlor, both stabilized chlorine sources and both acidic! Having a high TA will cause more outgassing of CO2 and create a tendency for the pH to alway be rising toward aobut 8.2. This nicely offsets the acidic efficts of the trichlor or dichlor and helps maintain a stable pH. This is also why addition of baking soda to increase TA is a regular occuracne with stabilized chlorine and the use of muriatic acid is much less frequent but the opposite is true with unstabilized chlorine (including SWGs) where the use of muriatic acid to lower pH is the norm and very rarely does TA need to be increased (and when it is it is usually increased too much, leading to even worse pH instaiblity and scaling conditions since the pH now alway s wants to rise toward 8.2 until enough of the TA has been destroyed by the additon of acid to get the pH in line!)

Also, running your pH at 7.6 and NOT LOWER will slow the outgassing of CO2. The lower you place the pH the faster outgassing occurs. This is why we purposely drop the pH low when we want to lower TA! My rule of thumb is to keep the pH at 7.6 and when it hits 7.8 it's time to add enough acid to lower it back down to 7.6. A bit of trial and error will soon teach you how often and how much is needed!

Adding borates to your water in a 50 ppm concentration will help with pH stablilty with a SWG, particularly when the TA is run in the 70-90 ppm range jand pH is kept between 7.5-7.9 (a little wider window than without the borates!). There are several reasons why:
It introduces a secondary borate/boric acid buffer into the water which works in the oppsite direction of the carbonic acid/carbonate/bicarbonate buffer we call TA. Instead of moving the pH up it moves the pH down. This effectivly tends to 'lock' the pH around 7.6 to 7.7 for a long period of time compared to without the borates.

It has algaestatic properites so instead of relying on the chlorine to kill nascent algae blooms which are always occuring these are kept at bay. This allows you to run the cell at a lower output since it lessens the chlorine demand (sometimes by quite a lot!) Running the cell at a lower output causes less outgassing of CO2, etc., etc.


Finally, a few things about your ColorQ. Don't trust the CH test if your calcium levels by a titration test are within 100 ppm of the upper limit of the ColorQ (which means if your calcium when titrated is above 300 ppm!) This is a known problem with all of LaMottes colorimetric based CH tests that they do not like to disclose. I use LaMotte water testing at work and only after presenting them with repeated documentation of discrepencies between the results I obtained with their Waterlink Express and with EDTA based titrations for calcium hardness when calcium levels were high did they admit that the calcium test can become very inaccurate and read low when the calcium range is either higher than the meter's range or withing 100 ppm of the upper limit of the range! You should have no problems with the other tests in the kit but be aware that some of the precision ranges are greater than for the same tests done with a Taylor kit (CYA, TA, CH). This, once again is because of LaMottes colorimetric tests vs. a drop based titration test. (I'm talking about the TA test here).
The Chlorine and pH tests are going to be extremely accurate but be aware that the chlorine test is a DPD test so it is susecptible to bleach out when the chlorine levels are aboeve 10 ppm, leading you to believe that there is no chlorine in the water when the chlorine levels are actually high. This is not just a LaMotte problem but is common to all DPD chlorine tests (But NOT FAS-DPD titrationt tests for chlorine, nor OTO (yellow) tests for TC)
Also, be aware that pH should NEVER be tested when FC is above about 8-10 ppm because it will read high. Once again, not a LaMotte problem but just an interference between the phenol red indicator used to test pH in pools and levels of sanitizer.
Hope this is helpful.

P.S. I just want to add that I have a large customer base and have had many people come in with problems with their salt pools ranging from black algae and mustard algae! to just not being able to maintain any chlorine and by insuring that the CYA was within range (In EVERY case it was too low!) and maintaining proper pH (Many of them had pH readings of 8.0 and above) the problems were effectively solved (with what ever other treatments might have been needed such as maintaining high FC to kill algae, etc) and have not reoccurred. That alone has been enough to convice me that running the recommened CYA levels for a SWG is the right thing to do even if I did not understand the chemistry behind it!

I know this is old but thank you for this!!! Oldie but goodie!