SWG, ORP level, and chlorination relelation question

[PowerJ]

This is a general question about the process of how SWG work.

My SWG is set by ORP NOT by a % of time the pump runs. I know from research that ORP is a measurement of oxidation of chlorine and that an ORP reading of 750-800 is very clean water meaning that the sanitizer (chlorine?) is easily used. I know that pH affects the ORP level. Lowering the pH of the water should increase the ORP level. Please correct me if I am misunderstanding...

So how does this measurment of the usability of the chlorine (ORP) traslate into the production of chlorine?
For example, on my omnilogic I had a set ORP of 700mv and the actual ORP was 720mv. The SWG was not chlorinating at the time. I set the acid tank pH down to 7.3 from 7.5 and turned the ORPset point to 750mv. (The chlorinator turned on and started chlorinating.) That should have resulted in the ORP level increasing, right? And if Increasing the ORP set point from 700mv to 750mv increased the chlorination then why did the actual ORP level drop? How does the SWG know to produce more chlorine? If the answer to increasing the ORP level is to add chlorine, why did the ORP level drop? Am I missing something in how this process works? Can someone please clarify.

One of the main reasons we spent the extra $$$ to purchase a SWG system is because I thought that it is possible to run very low levels of chlorine in the pool if the ORP is high... Please do not tell me to turn off the SWG. I want to understand the process so I can manage it.

 

[Jimrahbe]

P,

You won't find many here that use the ORP system.. We don't recommend using it, but we do a few members that do. I say that just because it might take a day or so for one of them to reply..

Not many here would tell you to get rid of your SWCG, as it is one of our favorite way to chlorinate a pool. But our process requires a higher level of CYA than most ORP systems allow, and we have found, that over time ORP control causes many more problems, than it solves.

I suggest that you read through our Pool School and I think you will find that our goal is almost never to try to maintain the lowest possible level of FC.. Our main goal is to maintain enough chlorine so that our pools are properly sanitized, safe, clear, and algae free...

Thanks,

Jim R.

 

[PowerJ]

P,

You won't find many here that use the ORP system.. We don't recommend using it, but we do a few members that do. I say that just because it might take a day or so for one of them to reply..

Not many here would tell you to get rid of your SWCG, as it is one of our favorite way to chlorinate a pool. But our process requires a higher level of CYA than most ORP systems allow, and we have found, that over time ORP control causes many more problems, than it solves.

I suggest that you read through our Pool School and I think you will find that our goal is almost never to try to maintain the lowest possible level of FC.. Our main goal is to maintain enough chlorine so that our pools are properly sanitized, safe, clear, and algae free...

Thanks,

Jim R.

Thank you for your reply. Yes, I've read through Pool School but I will review it again, and again, and again.

So not all SWG use ORP or measure it? I assumed they all worked the same way...? I am not opposed to higher chlorine levels it is just that I thought if the ORP is high then that means the chlorine is doing its job sanitizing, keeping the pool safe, clear, and algae free regardless of the chlorine level. Is that wrong? That it is possible to have safe, low chlorine levels dependant on the ORP? But then that would also mean that it would be possible to have a very high level of chlorine that is useless if the ORP is too low (below 650 for pools)? This is why I am trying to understand how the measurment of a chemical reaction corresponds to the demand of the chemical in that reaction. How does the chlorinator know to produce chlorine? Is the Sense and Dispense measuring it? If so, what level is it set at? I just don't know how to get the chlorinator to produce chlorine needed based off of the ORP level. Shouldn't I be able to set it so that it produces 5ppm as an example, how do I tell it to do that? Even the Hayward manual refers to percentages. My PB is all but useless. He's the one who got me into this mess... Also if the SWG uses up the oxidized chlorine and turns it back into salt to produce more chlorine then why do I need to measure the TC? I would use that information to decide if the Chlorinator is able to keep up with the demand and then make the adjustment? But isn't that what the ORP would tell me? Can I assume that if the ORP level is low then the TC must be too high? Again if the sollution is more chlorine why did the ORP drop? Should that have happened? Maybe I should just call Hayward... "Piece of cake, super low maintanance, you will not even need a pool service..." said my pool builder!

 

[JamesW]

ORP really doesn't work well, especially if you have cyanuric acid in the water.

What is the cyanuric acid level?

Is the system set up correctly?

 

[JoyfulNoise]

This is a general question about the process of how SWG work.

My SWG is set by ORP NOT by a % of time the pump runs. I know from research that ORP is a measurement of oxidation of chlorine and that an ORP reading of 750-800 is very clean water meaning that the sanitizer (chlorine?) is easily used. I know that pH affects the ORP level. Lowering the pH of the water should increase the ORP level. Please correct me if I am misunderstanding...

Not quite...

ORP stands for oxidation-reduction potential and it is a measure of the tendency of any chemical species to either be oxidized (lose and electron) or reduced (gain an electron) in an aqueous environment. It is typically measured using a platinum or gold electrode that is compared to another reference electrode with a known potential (all of this is built into one small probe). So, an ORP probe doesn't measure any one chemical species specifically but rather the overall condition of the solution it is dipped into. When you place the probe into pool water it is telling you how easily an electron can be gained by the probe and thus how strongly "oxidizing" your pool water is.

So how does this measurment of the usability of the chlorine (ORP) traslate into the production of chlorine?

It doesn't.

ORP is a general characteristic of your pool water. Any oxidizer present will cause a change in ORP. So adding chlorine to the water raises the ORP voltage...but so does adding hydrogen peroxide, or bromine, or ozone, or UV light, etc, etc, etc.. Any oxidizing species added increases the ORP. As well, the condition of the water, ie, pH, TA, salinity, etc., affects the ORP voltage as well.

Finally, Cyanuric Acid, or stabilizer, changes (or reduces) the amount of available hypochlorous acid (HOCl) in the pool water. HOCl is the primary oxidizing species of chlorine in pool water. Therefore it's concentration is what the ORP sensor will react to. If there isn't enough of it in the water, then the ORP voltage reading will fluctuate and be more sensitive to other parameters like UV light or the presence of chlroramine, etc, etc..

In short, there is no direct 1-to-1 correlation between chlorine levels and ORP. In pool water, it becomes a very complicated mixture of multiple parameters.

For example, on my omnilogic I had a set ORP of 700mv and the actual ORP was 720mv. The SWG was not chlorinating at the time. I set the acid tank pH down to 7.3 from 7.5 and turned the ORPset point to 750mv. (The chlorinator turned on and started chlorinating.) That should have resulted in the ORP level increasing, right? And if Increasing the ORP set point from 700mv to 750mv increased the chlorination then why did the actual ORP level drop? How does the SWG know to produce more chlorine? If the answer to increasing the ORP level is to add chlorine, why did the ORP level drop? Am I missing something in how this process works? Can someone please clarify.

This is the problem with ORP control over your SWG running or not running - anything that affects ORP that isn't related to chlorine levels might cause the SWG to either run when it doesn't need to OR not run when it should.

A better, but far less desirable way to use ORP, is to treat it as a waring sign. You could run the SWG in a duty-cycle mode and measure your actual FC doing daily testing. Then, with the ORP simply as a readout, track ORP versus FC and look for a correlation. Then, once you understand your system better, you can test less often and use the ORP as a warning to either increase or decrease your SWG output manually.

One of the main reasons we spent the extra $$$ to purchase a SWG system is because I thought that it is possible to run very low levels of chlorine in the pool if the ORP is high... Please do not tell me to turn off the SWG. I want to understand the process so I can manage it.

You can only do this if your cyanuric acid levels are very low, typically below 20ppm. However, what will happen is your SWG will run constantly and you will wear out your salt cell faster than a typical SWG pool that simply uses a duty-cycle method and keep the CYA high.

Why??

Because SWG's add chlorine very slowly to pool water. SWG pools need high CYA levels to protect the chlorine generated from burning off in the sun. With no CYA or very low CYA, the chlorine put out by the SWG will almost instantly get used up. In the overnight hours, when pumps and SWG are not running, your pool water will be dangerously low in FC or not have any at all and that will lead to an algae bloom.

Sorry, but this is why TFP does not endorse the use of ORP as a control method for SWG systems nor the use of "low chlorine". There is nothing wrong with chlorine at any level as long as pool water chemistry is properly maintained. A swimming pool with 50ppm CYA and 3-4ppm FC has 17 times less hypochlorous acid concentration than a pool with 0 CYA and 1ppm FC. Pool's that follow TFP's FC/CYA ratio are far less harsh on the skin, eyes and bathing suits than pools that try to operate any other way.

 

[PowerJ]

ORP really doesn't work well, especially if you have cyanuric acid in the water.

What is the cyanuric acid level?

Is the system set up correctly?

This is what I was afraid of the more I learned about ORP. Why does Hayward use that measurement to control the chlorine? I would never have know to ask the PB to install a SWG that wasn't using ORP as the control....

The CYA is hovering around 30. My thoughts are that I may need to SLAM the pool.

How would I know if the system is set up correctly? I don't know what I don't know which is super frustrating and how I ended up here....

This has been helpful, thank you for the reply

 

[PowerJ]

This is the problem with ORP control over your SWG running or not running - anything that affects ORP that isn't related to chlorine levels might cause the SWG to either run when it doesn't need to OR not run when it should.

A better, but far less desirable way to use ORP, is to treat it as a waring sign. You could run the SWG in a duty-cycle mode and measure your actual FC doing daily testing. Then, with the ORP simply as a readout, track ORP versus FC and look for a correlation. Then, once you understand your system better, you can test less often and use the ORP as a warning to either increase or decrease your SWG output manually.



You can only do this if your cyanuric acid levels are very low, typically below 20ppm. However, what will happen is your SWG will run constantly and you will wear out your salt cell faster than a typical SWG pool that simply uses a duty-cycle method and keep the CYA high.

Why??

Because SWG's add chlorine very slowly to pool water. SWG pools need high CYA levels to protect the chlorine generated from burning off in the sun. With no CYA or very low CYA, the chlorine put out by the SWG will almost instantly get used up. In the overnight hours, when pumps and SWG are not running, your pool water will be dangerously low in FC or not have any at all and that will lead to an algae bloom.

Sorry, but this is why TFP does not endorse the use of ORP as a control method for SWG systems nor the use of "low chlorine". There is nothing wrong with chlorine at any level as long as pool water chemistry is properly maintained. A swimming pool with 50ppm CYA and 3-4ppm FC has 17 times less hypochlorous acid concentration than a pool with 0 CYA and 1ppm FC. Pool's that follow TFP's FC/CYA ratio are far less harsh on the skin, eyes and bathing suits than pools that try to operate any other way.
[/QUOTE]

Not quite...

ORP stands for oxidation-reduction potential and it is a measure of the tendency of any chemical species to either be oxidized (lose and electron) or reduced (gain an electron) in an aqueous environment. It is typically measured using a platinum or gold electrode that is compared to another reference electrode with a known potential (all of this is built into one small probe). So, an ORP probe doesn't measure any one chemical species specifically but rather the overall condition of the solution it is dipped into. When you place the probe into pool water it is telling you how easily an electron can be gained by the probe and thus how strongly "oxidizing" your pool water is.



It doesn't.

ORP is a general characteristic of your pool water. Any oxidizer present will cause a change in ORP. So adding chlorine to the water raises the ORP voltage...but so does adding hydrogen peroxide, or bromine, or ozone, or UV light, etc, etc, etc.. Any oxidizing species added increases the ORP. As well, the condition of the water, ie, pH, TA, salinity, etc., affects the ORP voltage as well.

Finally, Cyanuric Acid, or stabilizer, changes (or reduces) the amount of available hypochlorous acid (HOCl) in the pool water. HOCl is the primary oxidizing species of chlorine in pool water. Therefore it's concentration is what the ORP sensor will react to. If there isn't enough of it in the water, then the ORP voltage reading will fluctuate and be more sensitive to other parameters like UV light or the presence of chlroramine, etc, etc..

In short, there is no direct 1-to-1 correlation between chlorine levels and ORP. In pool water, it becomes a very complicated mixture of multiple parameters.



This is the problem with ORP control over your SWG running or not running - anything that affects ORP that isn't related to chlorine levels might cause the SWG to either run when it doesn't need to OR not run when it should.

A better, but far less desirable way to use ORP, is to treat it as a waring sign. You could run the SWG in a duty-cycle mode and measure your actual FC doing daily testing. Then, with the ORP simply as a readout, track ORP versus FC and look for a correlation. Then, once you understand your system better, you can test less often and use the ORP as a warning to either increase or decrease your SWG output manually.



You can only do this if your cyanuric acid levels are very low, typically below 20ppm. However, what will happen is your SWG will run constantly and you will wear out your salt cell faster than a typical SWG pool that simply uses a duty-cycle method and keep the CYA high.

Why??

Because SWG's add chlorine very slowly to pool water. SWG pools need high CYA levels to protect the chlorine generated from burning off in the sun. With no CYA or very low CYA, the chlorine put out by the SWG will almost instantly get used up. In the overnight hours, when pumps and SWG are not running, your pool water will be dangerously low in FC or not have any at all and that will lead to an algae bloom.

Sorry, but this is why TFP does not endorse the use of ORP as a control method for SWG systems nor the use of "low chlorine". There is nothing wrong with chlorine at any level as long as pool water chemistry is properly maintained. A swimming pool with 50ppm CYA and 3-4ppm FC has 17 times less hypochlorous acid concentration than a pool with 0 CYA and 1ppm FC. Pool's that follow TFP's FC/CYA ratio are far less harsh on the skin, eyes and bathing suits than pools that try to operate any other way.

This is all incredibly helpful and makes so much more sense as I learn about ORP. Thank you!!! However, this is way more involved than I would like to be. I thought I was on my way to establishing TFP balance for SWGs but then I got hung up on how to get the chlorinator to maintain the level that I want. I have foggy water, or water that is less clear than it has been. Anyway, I hadn't fully committed b/c I thought what good is doing everything I can to get it balanced and cleared if I don't understand how to keep it there with the SWG...

So really, I need to get a SWG that is not measured or operated by ORP? Do all Hayward SWG use ORP or did my PB go out of his way to select ORP? (I am waiting to hear back from my PB.) No wonder the pool service couldn't answer my questions.

Thank you again I very much appreciate the education.

 

[JoyfulNoise]

Someone who is an expert on Hayward's Sense 'n Dispense system will have to chime in. I know in the Pentair IntelliCHEM system, you can choose to either have the ORP probe control the SWG output OR you can simply set the SWG to run on it's stand-alone duty cycle and then just have the ORP report values. Hopefully the Hayward system gives you that kind of setup as well...if you have the user manuals they should explain the operating choices.

If the pool is cloudy, then you likely have the start of an algae bloom and the entire SWG system is useless anyway. SWG's can not get you out of an algae bloom, only a SLAM will do that. So you take the entire Sense & Dispense system offline for now and SLAM to pool. If you have automated acid additions, you do not want that running during a SLAM as the high levels of chlorine can lead to higher pH of the water and that will cause the acid pump to dump a lot of acid into the pool. Best to take the entire control system offline until you get the water cleared up.

 

[rlab]

@PowerJ you should be able to just do Omnilogic config -> config wizard - > Sense and Dispense -> "Does ORP control chlorinator?" just set this to No. The chlorinator will then go into manual mode based on the pump cycle, i.e. the TFP way of doing things.

You may want to get your installer to do this, as I think technically only qualified installers are meant to access these lower level Omnilogic settings.

 

[gwiddison]

I know this is an old thread but as many others seem to have been doing, have been trying to use ORP to control my pool Chlorine with a SWG, one reason I would like to do this is because of the fact that a: my property is rented out during the summer and b: I have an Abri (pool shelter), when the pool is covered it seems the chlorine does not "burn off" so will accumulate if not uncovered for a period, which does happen, if the SWG is left on a timer.
I, like the OP had the issue where when my SWG was turned on the ORP level actually dropped! after MUCH reading of ORP, SWG and anything I could find on the subject I saw a couple of posts saying that with a saltwater pool and SWG you need s gold ORP probe instead of the more usual platinum one as the hydrogen generated COULD affect the ORP readings although I could not seem to find any "official" documents that stated this.
I decided to try this anyway and after a bit of searching found an ORP probe with a gold electrode and fitted this to my system, the whole thing was instantly better and more stable, ORP goes up and down as expected during the course of the day and night, when the SWG is turned on the ORP No longer drops and although I accept that it may not be perfect it is definitely a lot better, I do find that the ORP also changes a bit with pump speed, when I run the pump slowly at night the ORP level drops slightly and exactly the reverse happens when I speed the pump up.
I also had a few other issues with fluctuating readings when I first installed the ORP controller but most of these were solved by bonding and the installation of an anode so I would also advise checking these when installing an ORP controller.
I am sure there is more to find out about all this but I do at last seem to have a system that is a lot more useable than before Hope this helps
someone!

Just a small update, after about a week with the ORP probe with the gold electrode instead of platinum my system does seem to be at a state where I am happy leaving it to do it's own thing, which is the first time I have been able to say that!
The ORP readings fluctuate quite a bit through the day which I am assuming is down to my CYA levels which are around 50%, in the day I think the FC bonds with the CYA so the readings go down. I have a STA-RITE SC75 which has 3 power levels, 33%, 66% & 100% I used to have this set high as the levels did not go up when it was running so I ended up with a very high chlorine level but low ORP, now I have it on 33% and my set point on my controller to turn this on is at 650mv, on this setting the SWG has been on for about 6 - 7 hours which equates to about 2 hours of chlorine generation which seems to keep my chlorine level according to the little test strips just about perfect! Today it is a bit cloudy so my ORP has not dropped very much which I think is correct.
I have a smallish pool, about 7m x 3m and also have a retractable pool shelter.

 

[clintwb]

I know this is an old thread but as many others seem to have been doing, have been trying to use ORP to control my pool Chlorine with a SWG, one reason I would like to do this is because of the fact that a: my property is rented out during the summer and b: I have an Abri (pool shelter), when the pool is covered it seems the chlorine does not "burn off" so will accumulate if not uncovered for a period, which does happen, if the SWG is left on a timer.
I, like the OP had the issue where when my SWG was turned on the ORP level actually dropped! after MUCH reading of ORP, SWG and anything I could find on the subject I saw a couple of posts saying that with a saltwater pool and SWG you need s gold ORP probe instead of the more usual platinum one as the hydrogen generated COULD affect the ORP readings although I could not seem to find any "official" documents that stated this.
I decided to try this anyway and after a bit of searching found an ORP probe with a gold electrode and fitted this to my system, the whole thing was instantly better and more stable, ORP goes up and down as expected during the course of the day and night, when the SWG is turned on the ORP No longer drops and although I accept that it may not be perfect it is definitely a lot better, I do find that the ORP also changes a bit with pump speed, when I run the pump slowly at night the ORP level drops slightly and exactly the reverse happens when I speed the pump up.
I also had a few other issues with fluctuating readings when I first installed the ORP controller but most of these were solved by bonding and the installation of an anode so I would also advise checking these when installing an ORP controller.
I am sure there is more to find out about all this but I do at last seem to have a system that is a lot more useable than before Hope this helps
someone!View attachment 420745

Just a small update, after about a week with the ORP probe with the gold electrode instead of platinum my system does seem to be at a state where I am happy leaving it to do it's own thing, which is the first time I have been able to say that!
The ORP readings fluctuate quite a bit through the day which I am assuming is down to my CYA levels which are around 50%, in the day I think the FC bonds with the CYA so the readings go down. I have a STA-RITE SC75 which has 3 power levels, 33%, 66% & 100% I used to have this set high as the levels did not go up when it was running so I ended up with a very high chlorine level but low ORP, now I have it on 33% and my set point on my controller to turn this on is at 650mv, on this setting the SWG has been on for about 6 - 7 hours which equates to about 2 hours of chlorine generation which seems to keep my chlorine level according to the little test strips just about perfect! Today it is a bit cloudy so my ORP has not dropped very much which I think is correct.
I have a smallish pool, about 7m x 3m and also have a retractable pool shelter.

Im Just here to comment and say I also have a small pool - about 2.5m x 6.5m and am attempting to get the ORP control set for similar reasons. I travel a lot so being able to monitor and let thing sort of self-adjust is very helpful.

I have the Hayward Sense and Dispense module connected to a Hayward AquaRite SWG and a Hayward PH Dispense module dispensing muriatic acid and this keeps my Ph very stable around 7.5.

My issue lately has been that my chlorine PPM keeps running WAY too high. Pool water looks pretty good but I’m reading 9ppm FC and 10pm total. So clearly that ORP is messing me up. Luckily it’s a small pool so changes happen quickly.

I am fine to keep learning this summer and if we can’t figure it out I’ll switch off the ORP control and just set it on a timer. But I would like to make it work if I can. Luckily the sense and dispense with the PH is flawless so it was worth it just for that.


I’m down in Texas where it’s HOT all summer long and constant 105°f and higher days in full sun is crazy but it’s ok

 

[Bperry]

Im Just here to comment and say I also have a small pool - about 2.5m x 6.5m and am attempting to get the ORP control set for similar reasons. I travel a lot so being able to monitor and let thing sort of self-adjust is very helpful.

I have the Hayward Sense and Dispense module connected to a Hayward AquaRite SWG and a Hayward PH Dispense module dispensing muriatic acid and this keeps my Ph very stable around 7.5.

My issue lately has been that my chlorine PPM keeps running WAY too high. Pool water looks pretty good but I’m reading 9ppm FC and 10pm total. So clearly that ORP is messing me up. Luckily it’s a small pool so changes happen quickly.

I am fine to keep learning this summer and if we can’t figure it out I’ll switch off the ORP control and just set it on a timer. But I would like to make it work if I can. Luckily the sense and dispense with the PH is flawless so it was worth it just for that.


I’m down in Texas where it’s HOT all summer long and constant 105°f and higher days in full sun is crazy but it’s ok

9ppm of FC is not very high if your CYA level is 60-70. Use the FC/CYA chart to check what the correct level should be.

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com