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Thread: Unexplained SWG differences from pool to pool

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    Unexplained SWG differences from pool to pool

    Split off of Downsides of SWGs, fact or fiction?. JasonLion

    It's apparent from this thread that there are unexplained differences in the results obtained from pool to pool. Three years ago I installed a Pool Pilot Digital SWG system. For 2 years, I added about 1 to 2 quarts of acid per week, after keeping the TA in the 70-80 range and keeping CYA around 80 to 100. I found on occasion that my lack of diligence on a daily basis allowed the pH to climib as high as 8.0. While with a liquid chlorine pool the lack of diligence results in a green pool, I found with an SWG the lack of diligence results in calcium deposits on the sides of the pool.

    Before the SWG, I would test the pool once a week when I added chlorine. With the SWG, I found I had better check the pH and TA on pretty near a daily basis, or else. This became something of a pain. And a disappointment, when despite my best efforts the pH still got way to high too many times (what can you do if you have a business trip that takes you away for a week), and damaged my pool surface (5 year old Marsite).

    So I decided to upgrade the Pool Pilot to a Total Control system, which controls pH automatically. The only part compatible with my existing system was the SC-48 cell, so the money spent on the basic system went to waste, since I would have purchased a TC system had I known of the constant demand for acid using the basic system.

    Results: much easier to deal with. The TC keeps the pool blue, and the pH under control. And I only test once a week, to make sure things are in line. And on a weekly basis, what I find is that I have to add Alkalinity Increaser to offset all the acid the TC pumps into the pool on a constant basis (when it drops to 40 or 50, I add 5# of AI to get it back to 70 or 80). And every month or so, I have to add acid to the acid tank. Over the past six months, I have added 65 pounds of Alkalinity Increaser and 20 gallons of acid.

    So, with a TC system, I find I can leave the pool to itself and test it once a week, and add something once a week. Same as with a pool without an SWG system. The weekly dose of Alkanlity Increaser is much easier to carry around than the weekly dose of liquid chlorine, and the TA does not rise as fast to alarming levels as the pH could in just a few days with a basic SWG. Score one for the TC over the SWG and liquid chlorine. But the monthly need to add 3 gallons of acid to the acid tank is unique to the TC pool. I guess you could compare that inconvenience to the need to shock a liquid chlorine pool occasionally. I've spoken to tech support about this, but there is no answer for my pool that they have. Maybe if some chemist came down and studied my pool as if it were his main job for a month, I'd get some answers as to why Waterbear's pool needs no attention and mine needs both attention and regular additions of chemicals. That's not going to happen, obviously.

    On balance, the TC pool I have is somewhat easier to take care of than when it was a liquid chlorine pool, so I'm keeping the system. But it's initial cost was significant, and I don't know that I would do it again. If any part of the system fails after the warranty runs out, I don't know that I'll spend the money to fix it.

    For those who don't have to add acid to an SWG pool, I'm mystified and disappointed I am not one of them. But for those whose pools will need acid (and you won't know until you install an SWG), it makes you wish for a way to add chlorine that does not require having to add chemicals on a weekly basis. Maybe that's just wishful thinking.

    As for the look and feel of the pool water improved with an SWG, that's hard to say. I'd like to think it's somewhat better, but if it is, it's not really obvious. In my pre-SWG days, I was pretty good about keeping my chlorine in the 3.0 range, so never really had any bad effects from too much chlorine. And my pool looked good then, and it looks good now.

    I keep a log of everything I add to the pool, and all test results. Goes back 4 years for my current pool, and several more before that on the pool at my former house. By now, it's quite a database. For what it's worth, I have a 17.000 gallon pool with an SC48 cell set to power level 1 - same as it was when it was a basic SWG system. The TC controls ORP and pH automatically. I have ORP set to 650, which roughly works out to 3.0 to 8.0 Free Chlorine levels (which I test weekly with a Taylor FC test kit).

    P.S. There are other details with a TC system that make it different from a basic SWG system: you have to keep the CYA at or below 60 to allow the ORP meter to work properly (it's unreliable with normal CYA levels), and the lower the pH the higher the ORP at a fixed level of Free Chlorine. That's good, because the higher the ORP, the less the SC48 works to generate chlorine and consequent acid demand. Thus, I keep CYA between 30 and 50, and set the TC to keep the pH at 7.40. (I tried raising that to 7.50 to reduce acid demand, but after a short delay the acid demand was equal to or worse than keeping it at 7.40, so I put it back. The higher the pH, the more the SC48 has to work to maintain an ORP set point). Supposedly, ORP is the real measure of anti-bacterial action, not Free Chlorine. There is a persuasive (but quite technical) explanation for that, which I'll leave to others.
    17,000 gallon in-ground Marsite pool
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    JasonLion's Avatar
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Warlord46
    There is a persuasive (but quite technical) explanation for that, which I'll leave to others.
    Actually, there isn't. There is a paper written by an employee of a company that pushes ORP sensors that appears to say that, but when you look into the details the available data does not actually support this conclusion.

    Acid demand does vary from pool to pool. In nearly all cases we have been able to get the acid demand down to levels that are low enough that it might as well not be there. But it doesn't always work, some pools still have a noticeable acid demand even after using the various tricks.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Warlord46
    Supposedly, ORP is the real measure of anti-bacterial action, not Free Chlorine. There is a persuasive (but quite technical) explanation for that, which I'll leave to others.
    The real measure of anti-bacterial action is most likely to be that of the hypochlorous acid concentration which is roughly proportional to the FC/CYA ratio. This is the basis for the chlorine/CYA chart, though the inhibition levels are targeted to prevent algae growth since algae is far harder to kill than most bacteria (so algae inhibition levels easily kill most bacteria).

    You can see that ORP and hypochlorous acid (not FC alone) are correlated in this post of real-world pool data though there is a lot of noise from ORP measurements, especially at lower ORP levels (same reasoning as to why your sensor doesn't operate well at higher CYA levels). There are substances such as MPS non-chlorine shock that will raise the ORP but will not kill bacteria nearly as quickly as hypochlorous acid so it is simply untrue that ORP is a measure of anti-bacterial action. ORP measures oxidation-reduction potential, but says nothing about the kinetics (speed) of such reactions nor their chemical selectivity (i.e. what they oxidize more readily) nor their ability to penetrate cell walls (i.e. is the substance charged), etc.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Downsides of SWGs - fact or fiction?

    You can see that ORP and hypochlorous acid (not FC alone) are correlated in this post of real-world pool data though there is a lot of noise from ORP measurements, especially at lower ORP levels (same reasoning as to why your sensor doesn't operate well at higher CYA levels). There are substances such as MPS non-chlorine shock that will raise the ORP but will not kill bacteria nearly as quickly as hypochlorous acid so it is simply untrue that ORP is a measure of anti-bacterial action. ORP measures oxidation-reduction potential, but says nothing about the kinetics (speed) of such reactions nor their chemical selectivity (i.e. what they oxidize more readily) nor their ability to penetrate cell walls (i.e. is the substance charged), etc.
    Well, looks like here we go with the details I mentioned in my last. Yes, ORP correlates well with the concentration of hypochlorous acid, which is the killing agent in free chlorine, as the second chart in your link shows. With just a FC test kit, you don't know what percentage of your free chlorine is composed of hypochlorous acid -- you just hope it's high enough. That is why ORP is a better measure of the killing potential of your pool water than a FC reading with a test kit. Bacteria, viruses, and algae are all killed by that acid, and it is quite true algae is hardier than bacteria. So I don't see why it is inaccurate to summarize by saying that ORP is a measure of the effectiveness of pool water to kill bacteria (or any other microrganism I could have mentioned). In a chlorine pool, the higher the ORP, the less time to kill a particular microorganism. Is there any disagreement on that? I am not aware of any test kit that measures the speed of chemical reactions, or the ability to penetrate cell walls -- or what biological processes are undermined once the cell is penetrated, or how the viral RNA is broken up exactly -- but I do not see that as a reason to give up testing for FC or ORP. Do we really need to know those particulars?

    Somebody else questioned the value of determining ORP as a measure of whether the pool needs more chlorine, without explanation. That is certainly contrary to what I have read in the available literature. And since ORP measurements are the only thing controlling the production of chlorine by my SWG, it is ORP measurements that are keeping my pool water blue, without my having to do anything to adjust chlorine levels with liquid chlorine or tablets for the past 6 months. My own experience therefore suggests there is a strong correlation between ORP and the killing power of the hypochlorous acid my system is producing for me. And my own checking of FC with a test kit confirms that my system is producing chlorine - some days as high as 8.0 FC, some days as little as 3.0 FC, with ORP set to 650.

    All of the above are side-issues to my main point, which I hope does not get lost in this minutia about ORP. My main point was that for my pool, I have not been freed from the obligation to periodically add chemicals to my pool with either a simple SWG system or a Total Control system. What has changed from my liquid chlorine days is which chemicals I have to add on a weekly basis. The weekly testing of the pool, trudging off the the pool store, adding the right amount of stuff weekly, has not changed. The chemicals I use now don't weigh as much as the chlorine jugs, so that's one good thing.
    17,000 gallon in-ground Marsite pool
    Hayward S310T sand filter
    Autopilot Total Control SWG system
    Pentair Whisperflow WFE-24, 1 HP pump
    AquaCal Heatwave Model 120 heat pump
    Jandy Pool Digital Assistant for remote programmed
    control of pool pump, heat pump, light, waterfall

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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Warlord46
    All of the above are side-issues to my main point, which I hope does not get lost in this minutia about ORP. My main point was that for my pool, I have not been freed from the obligation to periodically add chemicals to my pool with either a simple SWG system or a Total Control system. What has changed from my liquid chlorine days is which chemicals I have to add on a weekly basis. The weekly testing of the pool, trudging off the the pool store, adding the right amount of stuff weekly, has not changed. The chemicals I use now don't weigh as much as the chlorine jugs, so that's one good thing.
    I hear you loud and clear...

    The reason I manually dose is for convenience. I know it sounds contradictory, but let me explain.

    I got to this forum in the first place while searching for which SWG to buy. My search landed me here on this forum, and after reading not very much, I decided to buy a test kit, and switch from the trichlor tabs I had been using to liquid bleach while I researched the SWGs.

    With the help of this forum, and my handy test kit, I learned the true chlorine demand for my pool. Meanwhile, I'm reading about the various niggling problems people were having with their SWGs, and I have come to the conclusion that I don't want one after all. I test my pool water once a week and it is always where I expect it to be, but if I was relying on an electronic device to manage my water for me I would feel compelled to test much more frequently.

    For me, simplicity=reliability=convenience.

    Just another opinion...
    20K gal IG plaster pool, Manually chlorinated with 6% bleach, 1.5 HP Sta-Rite Dura-Glas II pump, Pentair FNS Plus 48 DE filter, Polaris 280

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    Re: Downsides of SWGs - fact or fiction?

    Of course, I reserve the right to change my opinion at any time...

    20K gal IG plaster pool, Manually chlorinated with 6% bleach, 1.5 HP Sta-Rite Dura-Glas II pump, Pentair FNS Plus 48 DE filter, Polaris 280

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    Re: Downsides of SWGs - fact or fiction?

    I hear ya...I was in Wal-mart today and they have the Intex SWG in the clearance aisle for $154... I was VERY tempted.....
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by frustratedpoolmom
    I hear ya...I was in Wal-mart today and they have the Intex SWG in the clearance aisle for $154... I was VERY tempted.....



    Resistance is futile......
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Warlord46
    Well, looks like here we go with the details I mentioned in my last. Yes, ORP correlates well with the concentration of hypochlorous acid, which is the killing agent in free chlorine, as the second chart in your link shows. With just a FC test kit, you don't know what percentage of your free chlorine is composed of hypochlorous acid -- you just hope it's high enough. That is why ORP is a better measure of the killing potential of your pool water than a FC reading with a test kit. Bacteria, viruses, and algae are all killed by that acid, and it is quite true algae is hardier than bacteria. So I don't see why it is inaccurate to summarize by saying that ORP is a measure of the effectiveness of pool water to kill bacteria (or any other microrganism I could have mentioned). In a chlorine pool, the higher the ORP, the less time to kill a particular microorganism. Is there any disagreement on that? I am not aware of any test kit that measures the speed of chemical reactions, or the ability to penetrate cell walls -- or what biological processes are undermined once the cell is penetrated, or how the viral RNA is broken up exactly -- but I do not see that as a reason to give up testing for FC or ORP. Do we really need to know those particulars?
    You are absolutely correct that it would be wrong to look solely at FC and have any idea of the disinfection/oxidation capability of pool water, and I never suggested giving up testing for FC. Rather, looking at FC AND CYA together, along with normal pH levels (somewhat near 7.5) DOES tell you the disinfection/oxidation level in the pool without needing an ORP sensor. This is because the amount of hypochlorous acid in the pool is strictly determined by a specific chemical equilibrium relationship between FC and CYA, known since 1974 and described and determined definitively in this paper.

    So though I agree with you that no one should be looking at FC alone, I strongly disagree with you that one should only be looking at ORP instead. One can look at FC/CYA and know very well what is going on in most cases (especially in residential pools). As I mentioned in my post, ORP can be readily fooled by other oxidizers in the water that are not sanitizers and do not kill pathogens quickly -- non-chlorine shock being just one example. A high ORP reading when non-chlorine shock is in the water does not mean that pathogens are getting killed that much more quickly -- the reading is falsely too high in this case with respect to pathogen kill rates. So yes, I disagree that high ORP always means the pool is sanitary. Also, such sensors are not typically very reliable or consistent (different sensors will get different readings of the same pool water -- that study I referred to showed that when looking at raw data for many pools that had additional sensors in their systems). This post shows that not only are the absolute ORP levels different from different manufacturers, but that even the slope of mV per chlorine level (with no CYA) varies significantly. The evidence from manufacturer studies (which are always to be questioned, in my opinion) correlating ORP to bacterial counts is roughly the same as that of calculated hypochlorous acid from the FC and CYA information (and pH, if available). So ORP, with no oxidizers in the water other than chlorine, isn't bad, but it's not superior either -- it really should be looked at as an automation control that you calibrate against known FC/CYA values and don't take an absolute mV reading as meaning very much by itself.

    I just don't want anyone to think that ORP is better than managing the FC/CYA relationship -- it isn't better (i.e. more accurate), at least not significantly, though is obviously automated. There are specialized hypochlorous acid sensors, but they tend to be even less reliable than ORP; otherwise, they would be even better to use for automation.

    You also mentioned the problems you were having with an SWG and having to check the pH and TA almost daily. Many of these issues have been figured out and mostly (though not completely) avoided through the techniques described in Water Balance for SWGs where using a lower TA target helps reduce the rate of pH rise in many of these pools as does having a higher CYA level (for pools exposed to a lot of sunlight), the use of 50 ppm Borates and targeting a slightly higher pH.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Downsides of SWGs - fact or fiction?

    Beez, problem with forums is that people rarely post positive stuff, they usually come here to search for answers to their problems. When everything is well, people don't even notice that SWG is there. If you compare amount of users complaining about SWGs on forums around the globe, with number of SWG owners it will be 0.1 or even 0.01% if not less.
    Even if you compare a number of problems people have with their pools on this forum vs the number of problems with SWGs, it will be the latter that wins.

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    Re: Downsides of SWGs - fact or fiction?

    Good point. And many times the problems with the SWGs turn out to be water chemistry/PO habits problems that can be easily resolved....
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Strannik
    Beez, problem with forums is that people rarely post positive stuff, they usually come here to search for answers to their problems. When everything is well, people don't even notice that SWG is there. If you compare amount of users complaining about SWGs on forums around the globe, with number of SWG owners it will be 0.1 or even 0.01% if not less.
    Even if you compare a number of problems people have with their pools on this forum vs the number of problems with SWGs, it will be the latter that wins.
    Your point is well taken, but I don't think I got my point across as well. What I'm trying to say is that my manual system is basically failsafe as long as I continue doing it. By adding bleach myself, I can absolutely trust what my FC level is without testing. I just don't believe I could trust an automatic system like that. Is it working today? Well, it was working to spec yesterday so surely nothing has changed, right? Maybe, maybe not...where's that ****ed test kit!!!

    But as I said, I may change my mind at any time...
    20K gal IG plaster pool, Manually chlorinated with 6% bleach, 1.5 HP Sta-Rite Dura-Glas II pump, Pentair FNS Plus 48 DE filter, Polaris 280

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    Re: Downsides of SWGs - fact or fiction?

    By adding bleach myself, I can absolutely trust what my FC level is without testing.
    You test your bleach, right?
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    Re: Downsides of SWGs - fact or fiction?

    So though I agree with you that no one should be looking at FC alone, I strongly disagree with you that one should only be looking at ORP instead.
    I think there is a fundamental misunderstanding here. I am certainly not advocating that people using liquid chlorine chuck their Taylor test kits and buy an ORP sensor. I agree that one can keep a pool blue and maintain a healthy dose of hypochlorous acid simply by monitoring FC, CYA, and TA and keeping those numbers within acceptable limits -- not a difficult task at all. I did it myself for many years, without even knowing what ORP was. Remember, my initial report was merely to inform the forum of one person's experience with both an SWG and a Total Control system, and the failure of the techniques of this forum to fully address the problems I was having with them. I did not intend to sing the praises of ORP sensing, and tried to avoid this tangent discussion about what it is and why it is used by the TC since these details were not germane to the point of my report.

    I only learned of ORP 6 months ago when reading up on how my Total Control system was designed to figure out how much chlorine to generate, without my having to manually program it as I did with the replaced SWG system. It's the machine that measures ORP, not me. It's the machine that uses ORP to determine how much chlorine to generate, not me. I don't say that measuring ORP is better than a Taylor test kit, it's just the way the machine works.

    And I have read this forum's advice on how to reduce acid demand in a basic SWG system. From formerly happy with TA at 120 in my liquid chlorine pool, I dropped it to 70-80 range to reduce acid demand once I started up the SWG system. It did a great job of reducing acid demand from some unholy high number to about a quart or two of acid per week. I didn't like handling that much acid on a regular basis, and the pH would swing very quickly with low TA, so I monitored it on a daily basis. If I ever left the house for a few days the pH would peg out high. When after 2 years I started finding deposits on my pool walls (due, I felt, for the number of times I had found the pH at 8.0 or higher), in my exasperation I went out and bought a TC system. It has done the job I bought it for superbly: taken over for me the task of rigorously keeping the pH where it is supposed to be, and keeping the pool blue -- all automatically. But it too needs to be fed acid, the only difference is I can pour it into the holding tank 10-15 gallons at a time, and forget it for a few months. The consumption of acid in my pool is phenomenal -- so high I have trouble keeping TA from falling below 50. Yet my pool's pH and chlorine (i.e.,ORP measuring hypochlorous) are always just fine. Whatever in the world has absorbed almost 3 years of that much acid without dissolving anything that falls into the pool, I have no idea.

    For those of you who don't have this problem, you are fortunate. And somebody made a good point that complaints are more likely to be posted than kudos. The problem as I see it is that you don't know what kind of pool you have until you spend the money and install the system, so you are flying blind when you get one of these machines. If the risk is low (and I don't know whether it is or not), it's probably a good idea to go ahead and install one. The only way to find out what the risk is, is to talk with professional maintainers of SWG/TC pools, who can describe the experience of their customers in bulk numbers and what percentage of them require large amounts of acid. You don't learn anything from anecdotal posts like this -- one way or the other-- about what such statistics are.

    I am sure there is a scientific explanation for all this, and I'd like to know what it is. The SWG manufacturer can't tell me, and I had hoped that they knew and could tell me what to do. If it was the marsite on my pool walls, I'd change it to something else. If it was running my pump longer, or shorter, I'd do it. If it was using some other acid instead of muriatic acid, I'd try it. If it was using softened water or hard water, I'd try it. If it was using the chlorine generator cell at a higher or lower power, I'd try it. If it was running my waterfall day and night, or never, I'd try it. If it was using an SC60 power cell instead of the SC48, I'd try it. If it was changing by sand filter to something else, I'd do it. But no such luck, they had no ideas. So, I buy acid and alkalinity increaser by the case.
    17,000 gallon in-ground Marsite pool
    Hayward S310T sand filter
    Autopilot Total Control SWG system
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Warlord46
    And I have read this forum's advice on how to reduce acid demand in a basic SWG system. From formerly happy with TA at 120 in my liquid chlorine pool, I dropped it to 70-80 range to reduce acid demand once I started up the SWG system.
    That is small fraction of the things that we suggest to do to keep PH under control in a SWG pool. Unless you have a negative edge, or some other source of extreme aeration, it is nearly always possible to get the PH completely under control. For a start you could try lowering TA to around 60 and adding borates. There are several other suggestions in the water balance for SWGs article, some of which you no doubt tried already, but it doesn't sound like you followed all of our suggestions.

    You won't be able to follow all of the recommendations as long as you are using the ORP monitoring portion of the total control system. One of the important ones is to raise the CYA level up to between 70 and 80, but the chlorine level management portion of the total control system does not work well at those CYA levels. Since the total control system is working for you as currently setup, it is much simpler to leave things the way they are. But if you wanted to explore the possibilities, I am confident that I could get your PH drift to be negligible with the total control system set to disable the ORP sensor and the CYA level increased and a few other tweaks. The PH regulation portion would still function as a backup.

    The chemistry is fairly well understood, though it does get rather complex. The majority of the PH increase comes from CO2 outgassing, which is significantly accelerated by aeration. Since the SWG produces hydrogen gas, which causes aeration, there is always some aeration with a SWG. The rate of PH drift is also linked to the TA level, higher TA levels cause more PH drift. Low TA levels have some minor problems of their own, but those can be eliminated by adding borates as an additional buffer system.
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    Re: Downsides of SWGs - fact or fiction?

    Quote Originally Posted by Beez
    What I'm trying to say is that my manual system is basically failsafe as long as I continue doing it.
    it's never failsafe when it's manual as it depends on you continuing doing it

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    Re: Downsides of SWGs - fact or fiction?

    Warlord46 it appaers that much of your pH increase is caused by aeration. The key is the reduction in your TA. You might try an experiment: let your TA fall as low as it wants. At some point the partial pressures of CO2 in the pool water and in the air will balance out, and your TA drop AND pH rise will slow. This should lower your acid demend, and of course eliminate your TA dosing. The downside is that your pH will move much quicker with smaller doses of acid. So while your acid demand will fall, the number of times you have to dose will increase.

    On my pool I have a similiar but somewhat different problem. I too have to acid large amounts of acid, however my TA is stable.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  18. Back To Top    #18

    Re: Downsides of SWGs - fact or fiction?

    There are several other suggestions in the water balance for SWGs article, some of which you no doubt tried already, but it doesn't sound like you followed all of our suggestions.
    Jason -- The only suggestion I did not try before switching from a basic SWG system to a Total Control system was the "optional" step of adding borates. I adjusted the CYA as recommended in the "Water Balance for SWG" post, I run my pump 12 hours a day, I kept TA under 90, and tried to keep pH between 7.5 and 7.6. As I said, with low TA the pH moved faster than in a liquid chlorine pool with TA at 120, with the result in my case of 8.0+ pH readings if I left town for 3 days or more. I had to monitor pH daily when home (which was most of the time), and add acid as needed, and I did it faithfully. Consequently, I found that it was much more difficult to maintain my basic SWG pool than my former liquid chlorine pool. Since I must use well water for all household water needs, my pool is filled with hard water with calcium at or above 400. That is what made it so sensitive to high pH -- the resulting scale caused me to give up on the basic SWG system.

    You had a good idea in your last post about running my TC system with the ORP turned off, which is something I have not tried. It will automatically add acid as needed, thus avoiding a scale problem. But I will go back to manually controlling the chlorine generator, which I was able to do without difficulty to keep FC at desired levels. That will allow me to reset CYA from 40 back to 70-80, and to reset the pH from 7.40 (to get a higher ORP) back to 7.5 to 7.6.

    That should reduce the acid demand back to what it was with a basic SWG system, but with pH automation so it never gets out of line as it did with a basic SWG system. But it won't cure the problem -- the only thing left is to try the borate option. I'll have to read up on why that might help, I don't understand the recommendation at the moment.

    Thanks for the good suggestion.
    17,000 gallon in-ground Marsite pool
    Hayward S310T sand filter
    Autopilot Total Control SWG system
    Pentair Whisperflow WFE-24, 1 HP pump
    AquaCal Heatwave Model 120 heat pump
    Jandy Pool Digital Assistant for remote programmed
    control of pool pump, heat pump, light, waterfall

  19. Back To Top    #19

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,085

    Re: Downsides of SWGs - fact or fiction?

    We don't really understand exactly why the borates help, but there are two possibilities that come to mind. First, is that it is known that the borates are a mild algicide so if there is any nascent algae growth in the pool, even if not visible, then the borates can help reduce chlorine demand from such growth and this lets you turn down the SWG on-time which slows the rate of rising pH attributable to the SWG (through whatever mechanism). Another possibility is that the borates somehow interfere with the carbon dioxide outgassing in some way thus slowing down the rate of pH rise.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  20. Back To Top    #20

    Re: Downsides of SWGs - fact or fiction?

    You had a good idea in your last post about running my TC system with the ORP turned off, which is something I have not tried. It will automatically add acid as needed, thus avoiding a scale problem.
    Well, I read the TC manual and find I must to correct the above assumption. The choice is either full automatic control of both ORP and pH, or manual control of both. That's very disappointing -- I see no reason why it could not have maintained pH automatically for me while giving me manual control of the chlorine generator. Having to monitor pH daily is what soured my on the basic SWG in the first place -- and I see that happening again. I am familiar with manually controlling the chlorine generator, but have no experience with how often to set the acid pump to run. Interesting, the TC manual had a guide: start with 5 ounces of acid per day per 10,000, or about 8 ounces per day for my pool, and adjust as necessary. That works out to almost 2 gallons per month. That is about what I was putting into my basic SWG pool -- so AutoPilot seems to suggest that my experience was typical. When I went to a TC system, the demand went to 3 gallons of acid per month (plus a weekly does of Alkalinity Increaser). That too should be expected, given the lower CYA and pH settings for a TC system. Perhaps my experience is not all that unusual after all.

    If by adding borates, I can get my acid demand down to adding acid rarely, then I won't need the pH function of the TC at all. Having the machine blindly adding acid to a pool that does not need it is as bad as adding none when it does. The system does allow for only manual chlorine generation, as if it were a basic SWG system. But then if I go that route and it works, I've wasted quite a bit of money upgrading from the SWG to the TC system. I'll have to think about this option.
    17,000 gallon in-ground Marsite pool
    Hayward S310T sand filter
    Autopilot Total Control SWG system
    Pentair Whisperflow WFE-24, 1 HP pump
    AquaCal Heatwave Model 120 heat pump
    Jandy Pool Digital Assistant for remote programmed
    control of pool pump, heat pump, light, waterfall

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