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Calcium & Magnesium

Discussion in 'Aquatic Plant Fertilization' started by rjordan393, Feb 17, 2015.

  1. rjordan393

    rjordan393 Guru Class Expert

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    Hello,


    Is it possible to have very little magnesium in my tap water that it does not show up in my tests. I have a LaMotte total hardness, calcium & magnesium by difference test kit. Before my last water change, I tested my tap water and the general hardness was 100 ppm as CaCO3. The calcium hardness was 100 ppm as CaCO3, leaving no room for magnesium. I may have performed the test incorrectly by mis-counting the drops. So to be sure, I will be testing again.


    On another matter, I think the ratio for calcium to magnesium is recommended to be 3.1 to 1. So I like to know if you agree with the following:


    PPM General hardness as CaCO3 minus PPM Ca hardness as CaCO3 = PPM Mg hardness as CaCO3.


    Ca hardness as CaCO3 divided by 2.5 = PPM Ca.


    Mg hardness as CaCO3 divided by 4.1 = PPM Mg.
     
  2. Solcielo lawrencia

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    My tap water, sometimes no Mg is detected. MgSO4 must be added.
     
  3. Tom Barr

    Tom Barr Founder
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    You can certainly have GH that is high Ca++, and little if any Mg. dosign GH booster at say 1-2 degrees dGH extra................prevents any such issues and offers no detrimental impacts on any plants, only benefits. the bad part, you need to add GH bostter. But DIY or vendor made GH booster is pretty cheap. 90$ and I have 150lbs worth.
     
  4. rjordan393

    rjordan393 Guru Class Expert

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    I posed my question on a chemical forum and was told that the calcium equation was acceptable but the magnesium equation is not. But one of my test kits indicates that it is. I guess it all depends on whose test kit one uses. But if one wants accuracy, it was suggested to find the molar mass of both MgCO3 and Mg. Then the equation will look like this: Molar mass of Mg / molar mass of MgCO3 = ........... * the difference between the general hardness minus the Ca concentration.


    Any online chemical calculator will or should give you the molar mass of any element or compound. For instance; the molar mass for CaCO3 is 100.0864 g/mol and for Ca it is 40.078 g/mol. But the molar mass for MgCO3 is 84.3139 and for Mg it is 24.305 g/mol. So as you see, the numbers will change for each element or compound. So one cannot use the same equations.
     
    #4 rjordan393, Feb 19, 2015
    Last edited by a moderator: Feb 19, 2015
  5. Tom Barr

    Tom Barr Founder
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    That's fine when dosing specific chemicals, however, to measure GH and Ca++ and Mg++ in aquariums, the test method, say using the Lamotte Calcium test uses the same method.


    So yes, depends on what you use to dose, same as it might if you dose say MgCl2 vs MgCO3.


    The test kit can still be used to measure the Ca and Mg individually in the tank.


    However, I do not think it is worth the trouble. Just dose a bit more and cover your bases and then no need to test.
     
  6. Benealing

    Benealing Junior Poster

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    I have very hard water. My tap is 13 drops dgH. I do not know the magnesium amount in the tap though. I am in central Indiana, so I assume most of the hardness is calcium from the limestone. I am dosing CSM+B every other day (1/32 tsp in a 20H). Should I be adding GH booster? I try to keep my tank at 7-8 dgH. Would adding a small amount of epsom salt cover the magnesium without other detrimental effects?


    Ben
     
  7. Tom Barr

    Tom Barr Founder
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    You could add a little epsom salt without any ill effect. It's more something to do that avoids the need to test, but prevents anything running too low. Less work an gets the job done.
     
  8. Benealing

    Benealing Junior Poster

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    Thank you. I have a 20H. How much would you add if this were your tank and your gH?
     
  9. Tug

    Tug Lifetime Charter Member
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    3/4 tsp would provide about 5ppm of Mg and ruffly 0.3 dGH
     
  10. Benealing

    Benealing Junior Poster

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    Thank you. Is there a target range for Mg that I should be aiming for, or is the 5ppm a catch all?
     
  11. Tug

    Tug Lifetime Charter Member
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    My understanding is that 5ppm is more then enough for a weeks supply.
     
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