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Old 03-02-2012, 10:12 PM   #1
Lodovico
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Default Anyone know how to calculate this?

Hi All,

I just got updated water numbers from the city and they don't have a reading for Magnesium which I know can be pretty important. I'm wondering if I give you the rest of my numbers, including total hardness, if anyone can give a rough estimate based on having all the other info.

Maybe this isn't possible,but I would really appreciate ate it if someone knows how. Thanks!

Calcium- 88 ppm
Sodium- 18 ppm
Sulfate- 56 ppm
Chloride- 40 ppm
PH- 7.5
Hardness as CaCO3- 243
Alkalinity- CaC03- 200

What's the magnesium??


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Old 03-02-2012, 10:33 PM   #2
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When a water authority doesn't report it that generally means that it isn't too significant.

All I can do is make the following assumptions
1. The 88 ppm is as Ca++ (not ppm as CaCO3)
2. The alkalinity titration was done to pH 4.3
3 There are no ions in the water except Ca++, Mg++, Cl-, Na+, HCO3-, CO3-. SO4--, H+ and (OH)-.

Based on that your magnesium is 13.4 mg/L.


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Old 03-03-2012, 03:51 AM   #3
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Quote:
Originally Posted by Lodovico View Post
they don't have a reading for Magnesium which I know can be pretty important.
I wouldn't categorize Magnesium as "pretty important". Trace amounts are all you need so single digit ppm are fine. The malt itself usually has enough Mg+ to take care of things.
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Old 03-03-2012, 05:08 AM   #4
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Most regulatory testing has reportable levels, so when an analyte is below a reportable level, it generally won't be reported.
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Old 03-03-2012, 12:34 PM   #5
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Not so. Many water authorities report ions below the MCL (or other limit). Besides which there is no MCL for magnesium other than indirectly through TDS/conductivity. Which is interesting as excessive Mg give lots of people the trots and makes the water taste bitter/sour.
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Old 03-04-2012, 02:40 AM   #6
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I was referring to a reporting limit which is usually determined by the quantitation limits of a method. Usually when a level is so low that it is indistinguishable from a blank measurement, it is considered below reportable levels. Below a certain point ions cannot be quantified with any degree of precision unless you are using some sort of ICP or AA METHOD and even those methods have their limits.
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Old 03-04-2012, 04:20 AM   #7
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Just went back and looked at the original post here. I learned
1. You have to read the post carefully
2. The report tells you what the magnesium level is:

Quote:
Originally Posted by Lodovico View Post
Calcium- 88 ppm
Hardness as CaCO3- 243
What's the magnesium??
Calcium at 88 mg/L corresponds to calcium hardness of 50*88/20 = 220 ppm as CaCO3. Total hardness is 243 which means that the magnesium hardness is 243 - 220 = 23 less the hardness from iron, strontium, copper .... That makes the magnesium 12.15*23/50 = 5.6 mg/L. This is subject to error if there are other polyvalent cations in the water but should be a much more accurate estimate than the electroneutrality one I gave earlier.


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