# Lamotte Ca Hardness, Ca and Mg levels



## dennis (Mar 1, 2004)

I know this has been discussed several times but I am still a bit confused so forgive me for rehashing the question.

I have the Lamotte Calcium Hardness Fresh and Salt water kit. Code 3609.

The freshwater instructions say: "the Titrator is calibrated in terms of hardness expressed as ppm CaCO3." It goes on to say "record the reading as ppm Calcium hardness as CaCO3."

Ok, that I understand.

On the saltwater instructions it reads basically:
-add 1ml aquarium water then dilute with distilled water to 12.9ml
-add everythign your supposed to and titrate
-at the color change, multiply titrator reading by 5.16, record as ppm Calcium as Ca++

That indicates you can find the amount of elemental Ca++.

So, if I wanted to know the Ca++ of my freshwater, for an undiluted sample I would take the reading as CaCO3, miltiply by (1/12.9) and multiply by 5.16 Correct?

Example: Freshwater sample, undiluted reads 75ppm as CaCO3.

75*(1/12.9)*5.16= 30ppm Ca++


If the above works, then finding Mg++ levels should be a snap. Working through the math it does not seem that way though. I know the mol mass of Ca is 40 and the mol mass of CO3 is 60 or, 1:1.5 Ca:CO3. So, so ppm Ca means 45ppm CO3. Add those together and subtracting from the original hardness mean that any difference is the amount of Mg as MgCO3 in the water. In my sample though, 30+45=75 so I have no Mg?

That can't be right.

I remember a formula where you could find the Mg from Ca and CaCO3 hardness but I can't find it now.

Anyone?


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## Salt (Apr 5, 2005)

In order to find magnesium hardness, you _must_ take a hardness reading with a GH test.

Lamotte's calcium test is a GH test with an inhibiting agent that prevents magnesium from affecting the test. There's no way you can find the magnesium level by using the calcium test alone.

I'm not sure why you are using that formula... keep it simple!  The calcium reading of the calcium test is in a CaCO3 equivalence. CaCO3 is 40.04320% calcium. So if the kit reads 75 ppm as CaCO3, then 75 * .4004320 = 30.0324 ppm actual calcium.

For magnesium, take your GH reading minus your calcium reading. For example, if your GH reading is 100 ppm as CaCO3, then 100 - 75 = 25 ppm magnesium as CaCO3. If you want to express this as actual magnesium, multiply by .2428391. So 25 * .2428391 = 6.0709775 ppm actual magnesium.

(In case you're interested, the .2428391 comes from the assumption that calcium and magnesium react equally on the GH test. Calcium weighs 40.078 grams per mole; magnesium weighs 24.305 grams per mole. Therefore, calcium weighs 1.64896 times more than magnesium (40.078 / 24.305). Take your 40.04320% calcium in calcium carbonate, and divide by 1.64896 = 24.28391%)


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## dennis (Mar 1, 2004)

Thanks Salt. I did not realize that Calcium Hardness was not the water hardness. I assumed it was one of those things like were we call alkalinity kH or carbonate hardness. You explanation makes a lot of sense. I think I'll print it out and stick your post in my test kit box


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## blondy33 (Jan 13, 2007)

oh salt thank you.
now i can calculate my calcium and magnesium.
i will keep this as note.


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## dennis (Mar 1, 2004)

So, one could use that to calibrate a standard Gh test kit, correct?

If I made a sample using CaCl2+2H2O and nanopure water, testing with the Ca Hardness kit should yield the same results (once converted to degrees) as the standard Gh test kit. Now, obviously the correct way to calibrate would be to make a known solution but if you did not have access to an accurate scale or something, this should work. It would only be as accurate as your Lamotte kit though. Of course, this solution would be a good way to check the Lamotte.

So, long story short. According to the Fertilator, 1gram CaCl2+2H2O (from Greg Watson) in 500ml water is 545.2mg/l Ca. Since Ca is .4 of CaCO3, then 545.2/.4= 1363mg/l hardness as CaCO3. 1363/17.86(mg/l per degree)= 76.3 degrees. Diluting 10ml of this with 90ml DI water= 7.63 degrees.

Correct?


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