Outdoor pool without CYA - will SWG wear down too quickly?

[mhca]

Hi

I live in Denmark with strict requirements on semipublic pools. We've therefore been required to have an automated system for measurement and dosing of chlorine and pH.

We had a professional pool company configure a system which was based around a Intellichlor IC40 SWG.
The measurement of chlorine was through an amperometric chlorine sensor. We first had one system and then another from Prominent was installed (Dulcometer).

We had a problem that both system after a few hours started measuring way too low levels of chlorine compared to the actual value.
Even though I had asked them a few times (I'm a complete amateur having studied only a little on the internet on our issues) if it could be related to the current CYA levels in the pool, they didn't really answer that and put focus on it. Levels were around 30 ppm CYA.

Suddenly they gave up on reinstalling different systems and sensors and they got to the clear conclusion that WITHOUT DOUBT this was due to cyanuric acid in the pool giving too low readings, something which was even mentioned in a small note in the first system's manual.

We have now drained the pool water completely and refilled with fresh water to remove CYA.
But now, my question, I am worried if the non-existent cyanuric acid will make the chlorine disappear constantly, thereby causing the SWG to run 80% of the day?
We will run at a Free Chlorine level around 1.5 mg/L as specified by our government.
I know it doesn't cost anything to produce chlorine with the SWG, but if the cell is worn down every year, then that's pretty costly.

What are you comments on this?

Thanks and best regards,
Martin from Denmark

 

[duraleigh]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Your thinking is correct. Without CYA, your SWG will have to produce A LOT (probably 3 times as much) more chlorine to keep the pool sanitized and you will quickly wear out the SWG cell.

We never suggest managing an outdoor pool without CYA.

 

[Bama Rambler]

Re: Outdoor pool without CYA - will SWG wear down too quickl

You are right about the sun burning thru the FC without any CYA but given the strict requirements you have, and the fact that the system won't work with CYA, you really have no choice but to run it to maintain the required FC.

I assume that the probe is working correctly without any CYA.

 

[mhca]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Thanks for the replies.

I was just wondering if the pool store has recommended a type of measurement and dosing controller which isn't suited for outdoor use.
They have a few times referred to large public swimming pools using the same equipment, but those are indoor pools and therefore don't need the CYA as they don't get any UV light.

I can't remember, but I think I read that amperometric chlorine sensors are generally not compatible with cyanuric acid. In one article, I read that generally around 20-25 PPM CYA or higher, sensors would give bad readings.
However, I once found a free chlorine sensor (which wasn't just ORP) which stated to be compatible with cyanuric acid.
Also through a quick Google, I found this one stating to be CYA compatible: http://www.sbcontrol.com/ppmsensors.htm
However, I don't know which sensors are recommendable and even which are compatible with the measurement and dosing controller.

Do you know if there are sensors for measurement of free chlorine which are more suited for outdoor pools?


Current we have a CLE3 Prominent sensor: http://www.prominent.co.th/product/pp/D ... ensors.pdf
And in the datasheets, it actually states that Cyanuric Acid will cause "damage of membrane".
They have been running this for 2-3 weeks in our pool before closing down and I wonder I we should claim to have a new sensor now that we start off fresh.

 

[chem geek]

Re: Outdoor pool without CYA - will SWG wear down too quickl

As for "damage of membrane" due to "organic chlorine disinfectants, e.g. cyanuric acid derived", this is ONLY for sensor type CLE 3, but not CLO 1, CLB 2-µA, CBR1, CGE 2. Note that sensor type CGE 2 is specifically designed to work in pools with CYA as they say that it measures, "Total available chlorine, such as organic chlorine-disinfectant like chlorine (iso-) cyanuric acid derivatives" and says they use a "hydrophilic membrane ensures Penetration of chlorine-(iso-) cyanuric acid derivatives to electrodes" and the chart on the next page has an "X" and not "damage of membrane" with regard to using CYA-based disinfectants (or really, having CYA in the water which is what they mean).

So you should NOT be using the CLE 3 sensor and instead should be using the CGE 2 sensor. Did they try that? If they did and it too did not work, then I suggest you just get an ORP sensor instead and create a setpoint relative to measuring the FC with wet chemistry. That's what most people do with chlorine automation and it works reasonably well so long as the CYA level isn't too high.

By the way, with 1.5 ppm FC and 30 ppm CYA and at a pH near 7.5, the hypochlorous acid and hypochlorite ion concentrations are each around 0.02 ppm. The ORP depends on the manufacturer, but will be on the order of 615 mV to 670 mV. If there were no CYA in the water, then 1.5 ppm FC would have around 0.75 ppm each of hypochlorous acid and hypochlorite ion (so 37 times higher) and the ORP would be on the order of 760 to 780 mV. This is all expected behavior and is one reason why when using CYA you want a higher FC level. With 30 ppm CYA, a commercial/public pool should probably have at least 3 ppm and possibly something closer to 6 ppm so that the hypochlorous acid level is closer to 0.1 ppm so is roughly equivalent to 0.2 ppm FC with no CYA. This is at the low-end of DIN 19643 (when ozone is also used; otherwise their minimum is 0.3 ppm) and the ORP is on the order of 680 to 720 mV.

The nice part about having CYA in the water is that you can have ample FC essentially "in reserve" to not run out locally while simultaneously having a lower active chlorine level so one has lower oxidation rates of swimsuits, skin and hair and a lower rate of creation of disinfection by-products and lower absolute levels of nitrogen trichloride. Supplemental oxidation systems such as ozone can then be used more effectively since the organic precursors and some initial chlorinated organics hang around longer to get handled by the ozone rather than continue to react with chlorine to produce the worst chlorinated disinfection by-products such as nitrogen trichloride, trihalomethanes (THM, though chloroform itself is not a problem), haloacetic acids (HAA5), and haloacetonitriles (HAN).

 

[mhca]

Re: Outdoor pool without CYA - will SWG wear down too quickl

As for "damage of membrane" due to "organic chlorine disinfectants, e.g. cyanuric acid derived", this is ONLY for sensor type CLE 3, but not CLO 1, CLB 2-µA, CBR1, CGE 2. Note that sensor type CGE 2 is specifically designed to work in pools with CYA as they say that it measures, "Total available chlorine, such as organic chlorine-disinfectant like chlorine (iso-) cyanuric acid derivatives" and says they use a "hydrophilic membrane ensures Penetration of chlorine-(iso-) cyanuric acid derivatives to electrodes" and the chart on the next page has an "X" and not "damage of membrane" with regard to using CYA-based disinfectants (or really, having CYA in the water which is what they mean).

So you should NOT be using the CLE 3 sensor and instead should be using the CGE 2 sensor. Did they try that? If they did and it too did not work, then I suggest you just get an ORP sensor instead and create a setpoint relative to measuring the FC with wet chemistry. That's what most people do with chlorine automation and it works reasonably well so long as the CYA level isn't too high.
....

Thank you for your thorough answer.
Regarding the 1.0-2.0 mg/L Free Chlorine, this is a government requirement and we cannot be outside this range. Therefore we must make sure that we are in this range since we will have random samples taken without warning by a third party company.

They did not try a sensor such as the CGE 2 sensor. I agree that it does sound interesting. In particular because it doesn't sound too ideal to run at zero CYA with the UV. The benefit on the other hand is only that the effectiveness of the free chlorine is higher with zero CYA.
However, I cannot really sort out how it would measure compared to a DPD1 test as this is what we will be qualified from? What is "total available chlorine" compared to normal total chlorine measured through DPD3?

Also regarding ORP measurements, these seem normal, although we again would have to have a knowledge person managing the pool to be aware that ORP isn't directly related to the free chlorine by itself, but that other factors also needs to be measured to calculate the FC from the ORP reading.

 

[chem geek]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Since you must be within 1-2 ppm FC, then you should have the lowest CYA you can measure which is 20 ppm in the better test kits and then 2 ppm FC with 20 ppm CYA would be equivalent to 0.1 ppm FC with no CYA. However, if you have high bather loads then you really need supplemental oxidation (ozone, UV) especially for indoor pools. Otherwise you would shoot for 1 ppm FC with no CYA. Unfortunately there is a factor of 10 difference in active chlorine levels between these and your government has such a narrow FC range allowed and no understanding of the chlorine/CYA relationship (that's pretty typical).

According to the CGE 2 sensor documentation, it sounds like it is measuring the same as the Free Chlorine from the test kits, the DPD1 test. The membrane lets hypochlorous acid, hypochlorite ion, and the chlorinated isocyanurates (chlorine bound to CYA) through, though I'm not clear how the "indirect amperometric measurement" is made to measure all these chlorine species combined. In their table what they list as "Free Chlorine" is implying measurement of hypochlorous acid and hypochlorite ion without chlorine bound to CYA. They have a different sensor, CTE 1, that measures Total Chlorine which includes combined chlorine (CC) or chloramines so is equivalent to the DPD3 test. Note that these two sensors say they cannot be used with saltwater chlorine generator (SWCG) systems. Their sensors measure the chemical species indicated below:

Sensor ... HOCl ... OCl^- ... Cl-CYA ... CC ... HOBr ... Br-DMH ... CB ... Comments
CLE 3 ........ X ........................................................................................ CYA damages membrane
CLO 1 ....... X ......... X ........................................................................... No membrane; measures same as DPD1 if no CYA is present; OK for SWCG
CLB 2-µA .. X ......... X ........................................................................... Low cost version of CLO 1 (connects only to compact controller); OK for SWCG
CBR 1 ........ X ......... X .................................... X .......................... X .... Has membrane; good for high pH; used for bromine with no DMH (no tabs)
CGE 2 ........ X ......... X .......... X ............................................................ measures same as DPD1 even when CYA is present
CTE 1 ........ X ......... X ........................ X ............................................... measures Total Chlorine same as DPD3 only when no CYA is present
CDR 1 ................................................................................................... Chlorine Dioxide (ClO₂) sensor
BCR 1 ............................................................. X ........... X ........... X ..... includes measurement of BCDMH (i.e. bromine bound to DMH as in tabs)
CLT 1 .................................................................................................... Chlorite (ClO₂^-) sensor
OZE 3 .................................................................................................... Ozone (O₃) sensor
PER 1 ..................................................................................................... Hydrogen Peroxide (H₂O₂) sensor
PAA 1 ..................................................................................................... Peracetic Acid (CH₃CO₃H) sensor
FLEP ....................................................................................................... Fluoride Ion (F^-) sensor

Key:
HOCl = Hypochlorous Acid (the disinfecting and oxidizing form of chlorine)
OCl^- = Hypochlorite Ion (not a strong disinfectant, but an oxidizing form of chlorine)
Cl-CYA = Chlorinated Isocyanurates (chlorine bound to CYA; not a disinfectant nor an oxidizer; holds chlorine in reserve that is released quickly)
CC = Combined Chlorine (both inorganic chloramines and chlorinated organics)
HOBr = Hypobromous Acid (the disinfecting and oxidizing form of bromine and OBr^- Hypobromite Ion is generally included in this but at pool/spa pH is in smaller quantity)
Br-DMH = Bromine combined with dimethylhydantoin as found in bromine tabs, where DMH is the bromine analogue to CYA for chlorine except bromine may not bind to it as much)
CB = Combined Bromine (bromine combined with ammonia and organics; bromamine, NH₂Br, is also a disinfectant unlike its chlorine cousin and is likely due to formation of Bromammonium Ion, NH₃Br⁺, that then forms ammonia and highly reactive bromine ion, Br⁺).

As for ORP, though it does not give a direct measurement of FC, it is fine for process control assuming your pH and CYA levels are not changing rapidly. So you just get your FC in line by measuring with your DPD1 test at a fixed CYA and pH level, then measure the ORP and use that reading as a setpoint that the controller will then use to dose chlorine to maintain that ORP. So long as the pH is reasonably maintained and the CYA level is not changing (which it won't since it only goes away from dilution and you will likely be using hypochlorite as your chlorine source), then the ORP is a reasonable proxy for maintaining the FC level. The main interference will be from a saltwater chlorine generator (SWCG) if the hydrogen gas bubbles from such a generator get too close to the ORP sensor. If you are using a sodium hypochlorite feed system, then this should not be a problem.

 

[mhca]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Since you must be within 1-2 ppm FC, then you should have the lowest CYA you can measure which is 20 ppm in the better test kits and then 2 ppm FC with 20 ppm CYA would be equivalent to 0.1 ppm FC with no CYA. However, if you have high bather loads then you really need supplemental oxidation (ozone, UV) especially for indoor pools. Otherwise you would shoot for 1 ppm FC with no CYA. Unfortunately there is a factor of 10 difference in active chlorine levels between these and your government has such a narrow FC range allowed and no understanding of the chlorine/CYA relationship (that's pretty typical).

Yeah, the government requirements are insane and far from reality. Don't know why they are so strict on a low FC level. 1-3 would be more fair and practical.

But since CYA so strongly reduces the effect of free chlorine (from how I understand your explanation), wouldn't we benefit from running at zero CYA considering that we are only allowed to stay at 1.0-2.0 ppm FC?
The only downside being that our saltwater chlorine generator will have to run more often and have to be replaced every ~2 years instead of every ~6 years?

According to the CGE 2 sensor documentation, it sounds like it is measuring the same as the Free Chlorine from the test kits, the DPD1 test. The membrane lets hypochlorous acid, hypochlorite ion, and the chlorinated isocyanurates (chlorine bound to CYA) through, though I'm not clear how the "indirect amperometric measurement" is made to measure all these chlorine species combined. In their table what they list as "Free Chlorine" is implying measurement of hypochlorous acid and hypochlorite ion without chlorine bound to CYA. They have a different sensor, CTE 1, that measures Total Chlorine which includes combined chlorine (CC) or chloramines so is equivalent to the DPD3 test. Note that these two sensors say they cannot be used with saltwater chlorine generator (SWCG) systems.

Where do you have the latter/bold information from?
The two sensors you are referring to, is that also including CGE 2 sensor?
Because it is an indispensible requirement for us to use a SWCG as we are not allowed to store any liquid hypochlorous acid while also having sulfuric acid which we use for pH.

I also found some information last night about the CGE 2 sensor and that it should measure identically to the DPD1 test.
We have a Lovibond MD200 5in1 photometer, so we are able to perform all the same standard tests as the company who does samples from our pool once in a while, apart from the THM test.

 

[JasonLion]

Re: Outdoor pool without CYA - will SWG wear down too quickl

But since CYA so strongly reduces the effect of free chlorine (from how I understand your explanation), wouldn't we benefit from running at zero CYA considering that we are only allowed to stay at 1.0-2.0 ppm FC?

No. FC at 1-2 with zero CYA is actually too high of an active level. Adding just a little CYA both greatly reduces chlorine loss to sunlight and it switches some of the reaction rates around so that less of some of the dangerous kinds of CC are created and instead some of the harmless forms of CC are preferred.

In addition to some of those sensors having problems with CYA, several of them have problems with SWG salt levels. I believe chem geek is saying that both CTE 1 and CGE 2 have problems with salt at SWG levels.

 

[chem geek]

Re: Outdoor pool without CYA - will SWG wear down too quickl

In the link you gave, the sensors that use a membrane including CLE 3, CBR 1, CGE 2, CTE 1 all have an "X" by the disinfectant type that says "chlorine gas, hypochlorite, electrolysis with diaphragm" but no X by the disinfectant type "electrolysis without diaphragm, electrodes in process". You should ask them exactly what this means and which category a standard saltwater chlorine generator falls into. I don't really know but assumed that a standard SWCG was "electrolysis without diaphragm, electrodes in process". I'm guessing that perhaps the higher salt level in an SWCG pool is the problem though maybe it's the hydrogen gas that they are worried about.

As Jason wrote, 1 ppm FC with no CYA is a higher active chlorine level than needed. A higher active chlorine level results in chlorine reacting faster with everything it comes into contact with including swimsuits, skin and hair and in the creation of disinfection by-products, though for the latter it also depends on the quantity of organic precursors in the water and in a high bather-load pool you should be removing the latter by water dilution, coagulation/filtration and/or secondary oxidation (e.g. ozone, UV).

 

[mhca]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Geez I'm tired of this complicated pool setup, and that the pool company haven't been better at advising us and configure a complete system suited for our needs.

I just read this brochure from Prominent: http://share.prominent.com/Product-Cata ... lume-2.pdf
On page 16 in the PDF is stated The DULCOTEST® chlorine measurement can also be used in sea water and brine baths.

From that information it sounds like the CGE 2 is also compatible with salt water applications.

I doubt that the pool company will agree if we suggest that they replace the CLE 3 sensor with a CGE 2, but to me it simply sounds like a better options since it would allow us to add maybe just 10-20 ppm CYA which can stabilise the chlorine and also possible let us end up at an active chlorine level as needed.

Our pool is not heavily used and load us typically not high even on weekends with great weather.

Best regards, Martin

 

[chem geek]

Re: Outdoor pool without CYA - will SWG wear down too quickl

Well, that sounds like the sensor is OK with salt, but as I pointed out electrolysis also produces hydrogen gas and maybe that's a problem -- I really don't know and perhaps you should call Prominent directly to find out about that.

Yes, if the CGE 2 were to work then you'd have greater flexibility to be able to tune in your active chlorine level. With a low-to-moderate bather-load as you describe, I don't think there will be much reason to have a higher active chlorine level and you probably won't need any supplemental oxidation. The FC that is around 10% of the CYA level should be more than enough for your situation. By comparison, the residential pools with saltwater chlorine generators operate at around an FC that is 5% of the CYA level which is enough to prevent algae growth in such pools, but they usually have 80 ppm CYA with 4 ppm FC to significantly reduce the SWG on-time.

 

[mhca]

Unhealthy for the SWG to be turned on and off constantly?

OK, just another thing.

We have the system up and running and water temp has just increased above the min. temperature for the IC40 to produce Cl.

What I noticed however, is that the Dulcometer D2C is only offers a Proportional or PID-control, but not On/Off control as our previous dosing system did.
The D2C has a cycle time of 30 seconds and PID parameters can not be adjust to such a degree that the IC40 is turned on completely and undisturbed unless the difference between the measured value and the setpoint is larger than 0.10 ppm.

When the setpoint-measured_value<0.10 PPM, the load% on the SWG is proportionally between 10% and 90%.
At 10% the chlorinator will be turned on for 30 seconds (cycle time) and then turned off for 9*30 seconds. Likewise at 90% load it will be turned on for 9*30 seconds and off for 30 seconds. At least that's what I could conclude from observing the system.

The IC40 has a startup time of 2 minutes to diagnose the flow, temperature and salt level, so the first 4*30 seconds it will not produce any chlorine.


Won't the IC40 SWG be stressed by this? Turning on and off?
Will it be worn down? The cells might not, if they don't turn on until after 2 minutes, but I'm guessing the salt, flow and temperature sensors may be stressed + the power center.

With automatic chlorine control, I would expect that quite much of the time, the chlorine should be within 0.10 ppm of the setpoint, and therefore I don't find this to be OK.

What do you think? Is this acceptable?

 

[chem geek]

Re: Unhealthy for the SWG to be turned on and off constantly

The IC40 has a startup time of 2 minutes to diagnose the flow, temperature and salt level, so the first 4*30 seconds it will not produce any chlorine.


Won't the IC40 SWG be stressed by this? Turning on and off?
Will it be worn down? The cells might not, if they don't turn on until after 2 minutes, but I'm guessing the salt, flow and temperature sensors may be stressed + the power center.

With automatic chlorine control, I would expect that quite much of the time, the chlorine should be within 0.10 ppm of the setpoint, and therefore I don't find this to be OK.

What do you think? Is this acceptable?

Sorry to take so long to respond to this last post which I had missed before, but saw again recently.

Most SWG cycles are on the order of 15 minutes to an hour or two, not 30 second time slots where 50% would be on for 2-1/2 minutes and then off for 2-1/2 minutes. There is usually a trade-off between too long a cycle that could build up too much calcium carbonate scale at the hydrogen gas generation plate vs. short cycles that may wear on the plates more. The cycle is to reverse polarity. Perhaps this manufacturer has determined that this shorter wear cycle does not adversely affect their plates -- I don't know.

Not the definitive answer you were probably looking for. It's really a question for the manufacturer of the SWG to answer.