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Old 08-24-2011, 03:56 PM   #1
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Default Total Alkalinity, CaCO3 as a function of Bicarbonate, HCO3

My most recent Lab Wards report shows my Total Alkalinity, CaCO3 as 89, my Bicarbonate, HCO3 as 97 and my pH as 8.1.

I had read that for pH under 8.3 Total Alkalinity, CaCO3 = 50/61 * Bicarbonate, HCO3. That does not hold true for my numbers. My report also lists Carbonate, CO3 as 6. Does that explain why the math doesn't work out? If so, is there a formula that calculates Total Alkalinty as a function of Bicarbonate plus Carbonate?

My Cations / Anions , me/L are 2.5/2.5 which gives me confidence that my test results are valid.

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Old 08-24-2011, 04:09 PM   #2
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Either the pH is in error or it was miss-keyed when entered in the program. For the reported HCO3 and CO3, the pH would have to be 9.1. If the pH is actually 8.1, then the HCO3 and CO3 would be about 107 and 0.6, respectively.

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Old 08-24-2011, 04:30 PM   #3
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Originally Posted by mabrungard View Post
Either the pH is in error or it was miss-keyed when entered in the program. For the reported HCO3 and CO3, the pH would have to be 9.1. If the pH is actually 8.1, then the HCO3 and CO3 would be about 107 and 0.6, respectively.

How about this one (all in mg/l - I think that's the same as ppm)

Calcium 1.59
Magnesium < 0.100
Alk as CaCo3 190
Ca++ hardness 3.98
Total hard CaC03 3.97
pH 8.80

Any ideas on how to treat this with 10% phosphoric acid ?

Want to get to a 6.00 pH for my mash water.........5.20 pH for sparge water

Should I treat the water over a period of 1-2 days to check where the pH is - maybe let the water stabilize

Thanks in advance for help
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Old 08-24-2011, 04:53 PM   #4
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That is an approximation and the closer you get to 8.3 the worse it becomes. Nonetheless I have long noted that Ward Labs alkalinity, bicarbonate and carbonate numbers do not jive. For example, I found a Ward Labs report under Brew Science where the Alkalinity is listed as 199, the bicarbonate as 231 and the carbonate as 6. Ordinarily, the alkalinity titration is done to 4.3 (in brewing). If this were the case, the bicarbonate would, for a pH 8 water, be 239 and the carbonate 1 mg/L. If I tweak the titration pH down to 3.77 then the bicarbonate becomes 231 but the carbonate stays right around 1. Ward Labs may be overlooking the fact that distilled water has intrinsic alkalinity of 2.5 ppm as CaCO3 to pH 4.3 (because you must add that much acid to pure water to lower its pH to 4.3) but that doesn't explain the discrepancy.

Furthermore, at pH 8 the ratio of bicarbonate to carbonate is (60/61)*10^(pH - 10.3756) =0.00414 regardless of how you define alkalinity and Ward Labs is coming up with something 6 times this. They can only do this by using a value for pK2 other than the correct one. Even putting in crazy temperatures does not let me come up with a pK2 that would explain this.

I have noted this discrepancy in every Ward Labs report I have checked. I always have been and still am mystified by this.

If you knock off the 2.5 ppm for the alkalinity of the water you get a bit closer to the correct number but not nearly as close as one would hope. I have no idea how they calculate the bicarbonate and carbonate numbers. It's usually done from the alkalinity in which case they are off quite a bit esp. WRT to carbonate.

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Old 08-24-2011, 05:39 PM   #5
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Nonetheless I have long noted that Ward Labs alkalinity, bicarbonate and carbonate numbers do not jive.
Can I put faith in any of these 3 numbers? Is it more likely the reported carbonate value is suspect?
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Old 08-24-2011, 06:10 PM   #6
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Carbonate would not be at issue for brewing so use either the alkalinity or the bicarbonate number. At the level of accuracy we deal with here it shouldn't matter. The alkalinity is the easiest to measure and they probably do that with an automatic titrator so perhaps that's the best one to use.

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Old 08-24-2011, 07:42 PM   #7
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jmf143:

I suggest you go with your measured test results - that is your actual data. Certainly there can be noncarbonate sources of alkalinity, so the data points to those as being present.

These are not great links, but they do at least provide some reassurance that non carbonate alkalinity is real.

This one hints at the relationship between calculated and actuual total alkalinity:
http://steamofboiler.blogspot.com/20...carbonate.html

Here is the abstract for the other link:
Total alkalinity (TAlk) has long been used to evaluate the buffering capacity of aquatic
systems. TAlk has also been used, together with measurements of either pH or dissolved
inorganic carbon (DIC), to indirectly estimate the partial pressure of carbon dioxide
(5 pCO2) in inland waters, estuaries, and marine systems. These estimates typically
assume that carbonate and bicarbonate ions comprise nearly all the species contributing
to TAlk; however, other inorganic and organic acids have the potential to contribute
significant non-carbonate alkalinity. To evaluate the potential for error in using TAlk to
estimate pCO2, we measured pH, TAlk, and DIC in samples of river water.
http://www.biogeosciences-discuss.ne...-5159-2011.pdf

What is your water source?

Cheers!

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Old 08-24-2011, 09:07 PM   #8
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There should be no buffering system in potable water other than carbonic/bicarbonate/carbonate (with the exception of the buffering capacity of water itself which is responsible for the 2.5 ppm as CaCO3 referenced in the earlier post). If there is I would suggest not brewing with or drinking that water until the source has been identified.

I note again that there are discrepancies in all the Ward Labs reports I have looked at but there are no discrepancies in water that has been analyzed by either me or other laboratories/agencies.

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Old 08-25-2011, 12:26 AM   #9
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Quote:
Originally Posted by Brewer3401 View Post
How about this one (all in mg/l - I think that's the same as ppm)

Calcium 1.59
Magnesium < 0.100
Alk as CaCo3 190
Ca++ hardness 3.98
Total hard CaC03 3.97
pH 8.80
There is a lot of data missing from that report. To come close to balancing, there would have to be a lot of sodium or potassium in the profile. It looks like water softener water. The bicarb shows about 219 ppm and carbonate is about 6 ppm at that pH. I'm doubting that this is a suitable brewing water.
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Old 08-25-2011, 12:07 PM   #10
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Quote:
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jmf143:

What is your water source?
My tap is in Wixom, Mi but the water is City of Detroit water, drawn from Lake Huron.
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