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Thread: Antifreeze and Chlorine

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    Antifreeze and Chlorine

    Current Pool School recommendations for Closing an in ground pool says the following:

    Anti-freeze - I add pool/RV anti-freeze (not automotive!) to the pipes at the rate of one gallon per ten feet or fifteen feet of pipe. It is a great help to have a curved funnel to get the anti-freeze into the return line.
    However, as I note starting with this post, propylene glycol and chlorine may react with each other. This may not only create a huge chlorine demand though one that is seen as slow over an extended period of time (so a few ppm FC of extra demand for many months), but may also create chloroform which is an EPA-regulated chlorine disinfection by-product as part of trihalomethanes (THMs).

    While it makes sense to blow out lines and cap them, the use of antifreeze may be questionable unless that antifreeze is removed from the line rather than dumped into the pool water upon opening.

    The issue is not the propylene glycol itself which is non-toxic, but rather 1) whether chlorine reacts with it creating a slow-burn extra chlorine demand and 2) whether the by-products of such chlorine reaction include chemicals that are toxic at higher concentrations such as chloroform. It should be noted that "swimming pool anti-freeze" which is propylene glycol is sold on the market so it would be a bit surprising if it did react with chlorine especially if it were to produce chloroform. Perhaps for most people the reaction is so slow as to not have a noticeably higher chlorine demand and perhaps the reaction by-products are mostly chemicals other than chloroform.
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    Mod Squad jblizzle's Avatar
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    Re: Antifreeze and Chlorine

    This is very interesting as we have often in the past said not to worry about mixing the antifreeze into the water upon opening.
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    Re: Antifreeze and Chlorine

    Excellent Post Richard!
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    Re: Antifreeze and Chlorine

    Quote Originally Posted by chem geek View Post
    Current Pool School recommendations for Closing an in ground pool says the following:



    However, as I note starting with this post, propylene glycol and chlorine may react with each other. This may not only create a huge chlorine demand though one that is seen as slow over an extended period of time (so a few ppm FC of extra demand for many months), but may also create chloroform which is an EPA-regulated chlorine disinfection by-product as part of trihalomethanes (THMs).

    While it makes sense to blow out lines and cap them, the use of antifreeze may be questionable unless that antifreeze is removed from the line rather than dumped into the pool water upon opening.

    The issue is not the propylene glycol itself which is non-toxic, but rather 1) whether chlorine reacts with it creating a slow-burn extra chlorine demand and 2) whether the by-products of such chlorine reaction include chemicals that are toxic at higher concentrations such as chloroform. It should be noted that "swimming pool anti-freeze" which is propylene glycol is sold on the market so it would be a bit surprising if it did react with chlorine especially if it were to produce chloroform. Perhaps for most people the reaction is so slow as to not have a noticeably higher chlorine demand and perhaps the reaction by-products are mostly chemicals other than chloroform.
    The slow burn is interesting as SLAMing for me never worked last year....and same for this year. It just sucks down FC more than normal - that is IF IF IF I have that in my water.

    I will help for sure...standing by.
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    Re: Antifreeze and Chlorine

    It makes me wonder if not all propylene glycol is created equally and cheaper versions of it may cause a much faster consumption rate of chlorine. Or if the mixture of all of the ingredients in standard rv antifreeze react with chlorine, causing the breakneck consumption rate.
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    Re: Antifreeze and Chlorine

    I found from this paper that if glacial acetic acid (i.e. water-free acetic acid) is present as a catalyst, then the hypochlorite oxidation of secondary alcohols proceeds fairly quickly but also does not continue on with the haloform reaction to produce chloroform. I don't think you have acetic acid in your pool, but perhaps there is something else in the water that acts as a catalyst, albeit one that is not nearly as efficient as acetic acid.

    This book section describes when trihalomethanes (THMs) are formed but unfortunately does not indicate what would happen with propylene glycol though it does note that organics with acetyl groups (methyl ketones, but not acetone itself) likely react in the haloform reaction. This paper gives rate constants for the chlorination of hydroxyacetone, but it is very slow except at higher pH.

    So the good news from this may be that while there may be a slow conversion of propylene glycol into hydroxyacetone, the further reaction to form chloroform is exceptionally slow at pool pH. So the problem is primarily one of chlorine demand and not production of chlorinated disinfection by-products. Since only one and not four chlorine would be used in this case, that would be around 190 ppm FC so at 2 ppm FC per day "excess" chlorine demand that you are seeing (you see 1.5 ppm FC over 12 hours in an OCLT so I figure 1 ppm of that is "excess"), that would be 3 months though the rate would slow down over time. A water test would provide further confirmation of not producing chloroform and I've contacted a water test lab in the Cleveland area to see if they can perform a TTHM or chloroform test.
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    Re: Antifreeze and Chlorine

    Anecdotally, I have not seen a chlorine demand issue in my pool upon opening when antifreeze was allowed to go in the pool. Granted, this is my first year opening the pool where I know it was closed properly with FC near shock levels when closing. Had residual FC of 5 at opening (closed at ~12-14). My chlorine demand since opening has been fairly steady for 4 weeks, about 1 to 1.5 FC per day. Lower FC usage than normal summer maintenance but water temperatures have steadily been in the 50 F range, just breaking 60 this week. All 3 return lines had roughly 1 gallon or slightly more of RV antifreeze in them. I had intended on blowing the antifreeze out, not into the pool but failed to remember to do that, so it all went in the pool water this year. By now, if the propylene glycol was being broken down into chloroform or other THMs, I may or may not be able to detect them, depending on what reactions have or have not taken place. pH of the pool at opening was high 7s, I believe 7.8 and has been maintained between 7.4 and 7.8 since opening. It would be fairly easy at this point to have my pool water analyzed for TTHMs if you thought it would be worth it.
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    Re: Antifreeze and Chlorine

    If you didn't see extra chlorine demand, then it's probably not worth doing any testing. It may be that there is something in the pools that are seeing higher demand (not just for a week or so to clear up opening algae, but months of slow demand) where they have something catalyzing the oxidation of propylene glycol. Let's see what is going on in those pools and figure that out first.
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    Re: Antifreeze and Chlorine

    Mr gunite how many gallons do you think we're in your pool.... My pools been open for nearly a month and a half I wonder if I have knocked down the antifreeze too much I wonder if testing yours might be more insightful
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    Re: Antifreeze and Chlorine

    Quote Originally Posted by toofast View Post
    Mr gunite how many gallons do you think we're in your pool.... My pools been open for nearly a month and a half I wonder if I have knocked down the antifreeze too much I wonder if testing yours might be more insightful
    I'm guessing somewhere around 4 - 5 gallons of antifreeze went in the pool.
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    Re: Antifreeze and Chlorine

    So your post made me think even though I used 10 gallons I'm not so sure that all 10 gallons went in the pool.... I'm not sure I'm going to exactly remember at this point
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    Re: Antifreeze and Chlorine

    Quote Originally Posted by toofast View Post
    So your post made me think even though I used 10 gallons I'm not so sure that all 10 gallons went in the pool.... I'm not sure I'm going to exactly remember at this point
    That's exactly what I'm thinking as well. I know I used 8 gallons, but I was able to shop vac at least 3 - 4 gallons out through the skimmer before starting the system up. I was pretty proud of myself for remembering to do that since it was my first time opening and closing the pool.

    However, I didn't even think about starting the system up set to waste....I was just hoping and praying that the system actually ran after this bitter cold winter we had with 5+ feet of snow.

    Once I started the system up, and walked back over to the pool, I saw the big pink clouds in the water from each return jet....and I kind of just blew it off since the it says it's non-toxic. It's certainly discouraging though if nothing else.
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    Re: Antifreeze and Chlorine

    Let's not jump to conclusions just yet. Though it would seem to be a culprit at least for increased chlorine demand, let's see if the measured chemistry of the water supports this hypothesis. If it does, then we should change the recommendation to say that if anti-freeze is used then it should be collected from the piping upon opening and not allowed to mix into the pool water, at least not in large quantities. Quite frankly I think it's a good idea not to add anything to the water that isn't needed or that could have consequences regardless.
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    Re: Antifreeze and Chlorine

    My only concern is that I might be over the hump and will the test (that cost a fair amount of $$) be helpful this late in the game ?
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    Re: Antifreeze and Chlorine

    Yes because 1) the chloroform won't go away (it's not oxidized by chlorine) and only slowly outgasses from the pool and 2) if they can test for hydroxyacetone then that too may be the endpoint. So if they can test for end-products, that will help confirm what is going on even if you are past the chlorine consuming propylene glycol ---> hydroxyacetone phase. I got a quote that was quite reasonable for chloroform so I think that's worth testing so will get that going.
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    Re: Antifreeze and Chlorine

    Hi guys.

    I just want to check something. Both Toofast and Mr. Gunite said they bought "Super Tech" antifreeze from Walmart. Just to confirm, did you use THIS (pink) antifreeze (for RVS) and NOT automotive (blue) right?

    (If you used automotive instead, my "googlresearching" would suggest a toxic byproduct that would need to be drained.)
    Antifreeze0068113100234_180X180.jpg-2a6face4aba56fe9809e067bf5e3393b59d01ab4-optim-180x180.jpg

    ALSO, Chemgeek, there is another thread where the user reported a high chlorine consumption and high ccs...whereby he has started to wonder if antifreeze got in the pool (small size in terms of gallons, ergo perhaps a higher concentration if this is the culprit.)

    Just for your research/observation and to assist Fungi (user name, not the substance here is that link: http://www.troublefreepool.com/threa...566#post808566
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    Re: Antifreeze and Chlorine

    I used the Pink stuff, or something very similar...
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    Re: Antifreeze and Chlorine

    Would it be a good idea to amend the opening instructions to flush the antifreeze out of the system and pool by using "waste" when first turning on the pump if it's available on the system ??
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    Re: Antifreeze and Chlorine

    I used rv antifreeze from walmart. I believe it was the super tech stuff. I have two return lines, two skimmer lines, and a main drain. It took about 4.5 gallons to fill them all. Even if I opened to waste, I would still have over 2 gallons of antifreeze in the pool. I just started everything up, and let it all go in the pool. I didn't notice any excessive chlorine use or any cc's. I don't know if I'm the exception or the norm, but I don't plan to try to suck antifreeze out of my lines.


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    Re: Antifreeze and Chlorine

    Quote Originally Posted by Kiss4aFrog View Post
    Would it be a good idea to amend the opening instructions to flush the antifreeze out of the system and pool by using "waste" when first turning on the pump if it's available on the system ??
    Let's find out if this is the source of the problem first. Two pools are having their water tested by labs. That may give us some clues. In general though, it's a good idea not to add anything to the pool that you don't need and that would include anti-freeze. Setting the multi-port valve to waste will remove anti-freeze from the suction lines, but it won't do any good for the returns. For those one would need to capture what initially comes out in a large bucket, presumably before one raised the level of the pool water during spring opening.
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