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Thread: Sodium Hypo and pH, LeimLife

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    Sodium Hypo and pH, LeimLife

    Split by moderator from HERE as it contradicts with the chemistry and our teachings. jblizzle

    Liquid chlorine adds a lot of ph to water, and you will continue to use acid to bring that ph down. 110 alkalinity isn't too bad, especially if your using liquid acid to drop the ph, because it will also lower the alkalinity. Get a bucket of sodium bicarbonate if the Alkalinity gets to 80, high alkalinity locks in pH low alkalinity let's is drift.

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    Re: Sodium Hypo and ph

    Lowering alkalinity allows the ph to move more, higher alkalinity locks it in, if I remember my CPO class correctly.

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    Re: Sodium Hypo and ph

    Don't lower the alkalinity the ph will continue to move. Liquid chlorine has high ph lowering the alkalinity allows ph to move more. High alkalinity locks it in.

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    Re: Sodium Hypo and pH, LeimLife

    Quote Originally Posted by LeimLife View Post
    Liquid chlorine adds a lot of ph to water, and you will continue to use acid to bring that ph down. 110 alkalinity isn't too bad, especially if your using liquid acid to drop the ph, because it will also lower the alkalinity. Get a bucket of sodium bicarbonate if the Alkalinity gets to 80, high alkalinity locks in pH low alkalinity let's is drift.
    What in the world to you mean by "adds a lot of pH to the water"? Do you mean it increases the pH? Hypochlorite sources of chlorine increase the pH when added to the water, BUT the usage/consumption of chlorine is an acidic process that couteracts the original pH increase so the net result is close to pH neutral except for the small amount of excess lye. See this post that goes into the chemistry of both chlorine addition and chlorine usage/consumption.

    As for TA, you are not realizing that TA is not only a pH buffer but is also a SOURCE of rising pH in the first place due to carbon dioxide outgassing. Pool are intentionally over-carbonated not only to provide pH buffering but also along with CH to saturate the water with calcium carbonate to protect plaster surfaces. A high TA does NOT lock in pH because it is (again) a source of rising pH on its own. You can see in this chart how over-carbonated water at various pH and TA is compared to carbon dioxide in air. Generally speaking, it the pH is rising, one should lower, not raise, the TA level for greater pH stability. If one wants additional pH buffering without being a source of rising pH, then one can use 50 ppm Borates.

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    Quote Originally Posted by LeimLife View Post
    Lowering alkalinity allows the ph to move more, higher alkalinity locks it in, if I remember my CPO class correctly.
    Since you mentioned the CPO class, I suggest you read the first post in the thread Certified Pool Operator (CPO) training -- What is not taught.

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    Quote Originally Posted by LeimLife View Post
    Don't lower the alkalinity the ph will continue to move. Liquid chlorine has high ph lowering the alkalinity allows ph to move more. High alkalinity locks it in.
    Again, if the pH is dropping then a higher TA can help offset that both from pH buffering and from being a source or rising pH via carbon dioxide outgassing. However, if the pH is rising over time and one is using hypochlorite sources of chlorine, then the TA should NOT be raised. If anything, it should be lowered. The usage/consumption is acidic so hypochlorite sources of chlorine considering both addition AND usage/consumption are close to pH neutral. Dichlor is then actually net acidic, and Trichlor is more acidic than just considering its effects upon addition.
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    Re: Sodium Hypo and pH, LeimLife

    Easy there killer I learned from a different book.

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    Re: Sodium Hypo and pH, LeimLife

    No problem. Just want to make sure you reconsider what you have learned. The CPO class only teaches the pH of the chlorine sources in terms of what happens upon their addition and unfortunately does not teach what happens to pH when the chlorine is used/consumed. Obviously this latter process is important because chlorine is not just added to have the FC level go up and up and up forever. The FC is kept fairly stable because the chlorine gets used/consumed. To not consider the effect on pH of this half of the process completely throws off what happens in pools.

    Let's take a simple example of a pool with a 2 ppm FC per day chlorine usage and that uses a hypochlorite source of chlorine such as chlorinating liquid, bleach, or even Cal-Hypo or lithium hypochlorite but assume the pH changes only from addition and ignore what happens when the chlorine is not used/consumed. If I start with a TA of 80 ppm and pH of 7.5, then the pH would rise to 8.35 after just one week (even with a TA of 120 ppm and ignoring carbon dioxide outgassing the pH would still rise to 8.11), to 8.67 after two weeks, to 8.80 after three weeks, and to 8.87 after four weeks. Obviously that isn't happening in real pools. Instead, the usage/consumption of chlorine is acidic and the net result is close to pH neutral. Clorox bleach has the lowest "excess lye" so after one month the pH would rise to only 7.54. High quality chlorinating liquid (12.5% with a pH of 12.5) would have the pH rise to 7.61. Lower quality chlorinating liquid (12.5% with a pH of 13.0) would have the pH rise to 7.93. This pH rise is just from the excess lye. In practice, most pH rise is from carbon dioxide outgassing though that is partly controllable by having a lower TA level.
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    Re: Sodium Hypo and pH, LeimLife

    Take this example if you will. Fresh filled pool has source water of 180 alkalinity and 8 pH. Using the guide in the Taylor test kit I add (for scenario sake) 2 gallons of acid. It only drops the alk to 160 and ph is now 7.5.

    Or...

    I add the 6 gallons the table recommends to lower the alkalinity (again scenario sake not real) and now the alkalinity is 100 but pH is well below 7. Then, to raise the pH it calls for 35# of soda ash and the end result is 7.5ph and 180 Alkalinity.

    I think by leaving the Alkalinity higher you don't add soda ash to the water resulting in less TDS and one less step in obtaining bather comfort of 7.5ph Higher alkalinity drives the Ph up again and you are able to lower the alkalinity again with the first stated step above. Over time you would be able to lower the alkalinity without sacrificing the pools usability, clarity, or elevate the TDS.

    Your thoughts?

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    Re: Sodium Hypo and pH, LeimLife

    Your first option is the better one, and I think that is what is suggested on this forum.

    Otherwise you will use masses of chemicals that fight each other a certain amount. And you will create quite corrosive conditions in the pool by dropping the pH below 7.

    I have fill water with alkalinity so high, when I test it, I get a reading of "HI" on my tester. I think that means TA is well over 200. I start the season with an entire pool full of this stuff.

    I add acid to keep pH down to around 7.6. I regularly add children to the pool to aerate the water. Over a period of a month or so my TA has come down below 100 and my pH had stopped wanting to rise so fast. My acid use is much less now. So it works for me.
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    Re: Sodium Hypo and pH, LeimLife

    As a real world everyday example. I use bleach exclusively and have everyday for the last 6 years. I never have to adjust the pH! It stays dead on at 7.5. My TA runs about 70 ppm. I have a 6 year old gallon of muriatic acid at the house that I've probably used a pint of.

    In your two examples above you're missing a few important parts. For one you don't tell us what the source of chlorination is. That's important in order to figure out what happens next.

    In example one if you lower the pH and the TA is still 160 ppm, and you're using liquid for chlorination, then it won't be long before your pH rises to where you have to add more acid which further lowers the TA and you'll be repeating this until the pool reaches equilibrium. As Chem Geek said above, if you're not taking into account both sides of the equation then you're not understanding what happens over time.

    Even if you're using an acidic form of chlorination the pool will eventually reach a point where it's fairly in equilibrium. However the TA will be higher. There are exceptions to the above where some outside force is affecting the equilibrium and you either have to add base or acid occasionally (i.e. continued use of an acidic chlorine source keeps lowering the TA so you have to occasionally offset that with some additional TA).
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    Re: Sodium Hypo and pH, LeimLife

    Quote Originally Posted by LeimLife View Post
    Take this example if you will. Fresh filled pool has source water of 180 alkalinity and 8 pH. Using the guide in the Taylor test kit I add (for scenario sake) 2 gallons of acid. It only drops the alk to 160 and ph is now 7.5.

    Or...

    I add the 6 gallons the table recommends to lower the alkalinity (again scenario sake not real) and now the alkalinity is 100 but pH is well below 7. Then, to raise the pH it calls for 35# of soda ash and the end result is 7.5ph and 180 Alkalinity.

    I think by leaving the Alkalinity higher you don't add soda ash to the water resulting in less TDS and one less step in obtaining bather comfort of 7.5ph Higher alkalinity drives the Ph up again and you are able to lower the alkalinity again with the first stated step above. Over time you would be able to lower the alkalinity without sacrificing the pools usability, clarity, or elevate the TDS.

    Your thoughts?
    You didn't say how many gallons, but to get your results I have to assume 50,000 gallons. Adding 2 gallons of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to 50,000 gallons where the pH is 8.0 and the TA is 180 ppm will lower the pH to 7.17 and the TA to 160 ppm. In practice, the pH won't drop down that far because carbon dioxide will outgas a lot especially as the pH gets lower so you might end up at the 7.5 you describe or perhaps somewhat below or above depending on how long you wait to measure and how much aeration there is.

    If you were to add 6 gallons, then the pH is lowered to 6.57 and the TA to 120 ppm though again the pH would likely not be seen as getting that low and might be around 6.8 or so due to carbon dioxide outgassing. Here you are making the mistake of adding soda ash. Why are you doing that? This not only increases pH but also increases TA by MORE than Muriatic Acid lowers it. This is because soda ash is sodium carbonate and is identical to adding a pure base such as lye (caustic soda; sodium hydroxide) and an alkalinity up product (baking soda; sodium bicarbonate):

    Na2CO3 + H2O = NaOH + NaHCO3
    Sodium Carbonate (soda ash; washing soda; pH Up) + Water = Sodium Hydroxide (caustic soda; lye) + Sodium Bicarbonate (baking soda; Alkalinity Up)

    Do you see how insane the classic advice from the pool industry is? Add acid to lower the TA but that lowers the pH so to get the pH back up now add a base, but even worse than a base use something that INCREASES TA? Even if you were to use a pure base to raise the pH, this also raises the TA as well but about half as much as the soda ash but EXACTLY the same amount as the acid you added. So you don't want to add an acid and then a base even if it's a pure base. As you point out, all that ends up doing is create sodium chloride salt!

    Instead, what you want to do to raise the pH without changing the TA at all is to aerate the water and to do so at lower pH since this speeds up the outgassing process. Of course, if you don't want the pH to get so low as to potentially damage plaster or corrode metal then you don't want to add so much acid at one time. In your example, you'd add whatever amount of acid that gets your pH down to one level above what your test kit measures (but not below 7.0), so if your test kit can measure to 6.8 you would go to 7.0 while if it only goes down to 7.0 you would to go 7.2. 3 gallons would get you to 7.0 but with outgassing perhaps you'd use 4 gallons. You would then aerate the water using waterfalls, spillovers, fountains, jets, turning returns upwards running the pump on high, having kids splash in the pool, use devices attached to the returns (see Example #1, Example #2, Example #3, Example #4, and a video example). For commercial use, you might consider using an actual aerator and a compressor/air pump as used in ponds to add oxygen to the water (see this product or if you are really serious there's big pond aerators) -- the key being to get something that puts out a lot of air as small tiny bubbles since they have more surface area (churning the water's surface accomplishes something similar though not quite as efficiently).

    Note that you aerate the water just enough to get the pH to rise a measurable amount and then add more acid. You do not need to nor want to aerate until the pH gets a lot higher because the rate of carbon dioxide outgassing will be less at higher pH. You basically add acid to keep the pH low (say at 7.0) while aerating. You do this until the TA gets to where you want (and you can just calculate ahead of time how much acid that will be) and stop adding acid when you reach your TA target. Then just aerate to get the pH up at that point without changing the TA. This process was described in some of the links I gave earlier (for example, in this post in the "Acid Columning" thread I linked to in this post responding to another thread of yours and is also described in the Pool School article Lower Total Alkalinity).

    Note that the process I described is EXACTLY the same as your second approach except that it is accelerated to lower the TA faster. In your second approach, carbon dioxide outgassing is still occurring, just more slowly. Yes, you could instead have your TA be higher for longer and add acid over time to maintain the pH as your TA will slowly drop, but there are reasons you might not want to do that. If you have higher CH so that your saturation index is high, then you'll need to maintain a lower pH while that TA is high and that can mean adding acid FREQUENTLY which can be annoying. The same is true with trying to keep the pH lower to prevent metal staining if there are metals in the water (though normally one uses a metal sequestrant to prevent that). Or one may just not want to have to add acid so frequently or is not able to because one doesn't service the pool every day (say, a pool service). In these cases, you can use the procedure to more quickly lower the TA and then be done with it -- one then can have a more stable pH and not need to add nearly as much acid nor have to add it as frequently. Of course, one doesn't do this procedure blindly since if one has very high TA fill water without a pool cover and with a lot of evaporation and refill, then one may decide not to lower the TA all at once and just deal with regular acid addition.
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