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Thread: Chlorine Block

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    Join Date
    Aug 2015

    Chlorine Block

    Topic moved from this thread

    Wow some really bad advice on hear. Some folks need to stop listening to old wives tales. Yellow must defently does work. Second yellow out does not "suck chlorine" its an acid that destroys the membrane of an organic. When you have a cac derived from heavy organic load switching to liquid means nothing. Nor does the amount of chlorine added over a couple weeks. When this happens you need yo add any fast acting chlorine ie:shock consistantly over a 24 hour period. Checking cya is a good thing. As for the statement they are going to tell you to drain your pool is silly.

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    Mod Squad tim5055's Avatar
    Join Date
    May 2014
    Franklin, NC

    Re: Chlorine Block

    Welcome to TFP!

    Yellow out is an ammonia based product, and as such "consumes" chlorine until the ammonia is gone. It does kill algae, but the recovery process,from using it can be as bad as the algae.
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  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Chlorine Block

    (NOTE: This thread is the one from 2010 to which the response by lawluck1 was made and moved here.)

    There is more than one Yellow Out product so which one specifically are you talking about? As shown in this MSDS for Coral Seas Yellow Out, it is 100% "Disodium salt of ethylenediaminetetraaceticaciddihydratediammoniumsulfate" so is a salt of EDTA combined with ammonium sulfate. Note that there is another Coral Seas product called Green to Clean with this MSDS that shows the ingredient is 100% "Disodiumsalt of ethylenediaminetetraaceticaciddihydratediammoniumsulfate" so appears to be the same. This expired patent from the Coral company describes the process where chlorine is added to ammonium to produce monochloramine.

    EDTA is often used as a metal sequestrant, but you need to read the Coral Seas Yellow Out instructions to see that you have the pH be high (>= 7.8) and add 2 pounds of Yellow Out product per 15,000 gallons, then add chlorine at a rate that works out to an increase of 6-15 ppm FC depending on the type of chlorine that is used (they are inconsistent in their instructions), then you add more chlorine again 12 hours and 24 hours after initial application.

    As described in this EPA document, EDTA by itself has some mild algaecidal properties where Table 4 shows a 50% kill of green algae over 96 hours at 3 mg/L of EDTA. The dosage of EDTA for Yellow Out is around 16 mg/L including the ammonium salt so around 11 mg/L of EDTA and 5 mg/L of ammonium sulfate. However, it is primarily the formation of monochloramine from the ammonium reacting with chlorine that is the primary algaecide, at least in the initial hours. The 5 mg/L of ammonium sulfate would react with 5.4 ppm FC to produce monochloramine as 5.4 ppm CC while any excess chlorine added would continue to oxidize the monochloramine more slowly (over hours) to nitrogen gas. The shock 12 and 24 hours later is to get rid of the monochloramine as well as get started on getting rid of the EDTA. Even intheswim notes the following:

    Chlorine Boosters: These are salts of EDTA and ammonium sulfates. Added to the pool before shocking, monochloramines are created, killing most forms of pool algae. See Green to Clean and Yellow Out.
    In addition to the very fast reaction of the ammonium sulfate with chlorine to form monochloramine within a minute or two, the EDTA also more slowly gets oxidized by chlorine creating chlorine demand for up to a week (or more, though their shock steps are intended to accelerate the oxidation of EDTA). This is why we recommend using HEDP-based metal sequestrants rather than EDTA because HEDP is more resistant to oxidation by chlorine compared to EDTA.

    Is the mild EDTA algaecide effect what you are calling "an acid that destroys the membrane of an organic"? It is not the fact that EDTA is an acid that has anything to do with its algaecidal properties. You can add Muriatic Acid to a pool and not kill algae. Also, the actual Yellow Out product has a disodium salt of EDTA, so it isn't even a strong acid (see this link showing the pK3 of 6.16); the ammonium ion is even more weakly acidic (pKa = 9.2) similar in acidity to boric acid (pKa = 9.1). The MSDS I linked to earlier says the pH of a 5% solution is > 4.8. As the EPA notes, the mode of action for EDTA is not known definitively, but it is likely that it is related to its chelating properties. As noted in this document, it is EDTA's metal chelating properties that likely lead to toxicity to algae if the amount of EDTA is significantly higher than that of trace metal ions essential to algae growth.

    The primary purpose of using an ammonium product to produce monochloramine is to work around high CYA levels since monochloramine, unlike chlorine, will not bind to CYA so will not be lowered in its strength. Also, while monochloramine is a slower killer of bacteria than chlroine, algae take up monochloramine as if it were an ammonia-based nitrogen food source. In fact, nitrogen plant fertilizer (remember that algae is in some ways similar to a plant) is derived from ammonia such as ammonium nitrate or ammonium sulfate (see this link).

    So an ammonium-based product will work to kill algae and work around high CYA levels but after you've killed off the algae you are still left with high CYA levels that were the source of the problem in the first place (unless one intends to maintain a high FC level for the appropriate FC/CYA ratio). So better long-term advice would be to lower the CYA level rather than add a workaround product such as ammonium. Another workaround product (such as United Chemical Algaecide products) uses sodium bromide to turn a pool into a bromine pool. This also works around CYA, but is more permanent since the bromine can take months to remove. So at least with the ammonium-based product you can get rid of it, but that doesn't change the fact that it is only a workaround and doesn't address the core CYA issue.
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