# Using CaMg(CO3)2 to buffer KH?



## Gumby (Aug 1, 2005)

I just recieved some CaMg(CO3)2 from Greg Watson and I intend to use it to buffer my KH. 

Does anyone know what amount of CaMg(CO3)2 would be required to raise the KH by one degree in 135gallons? I'm afraid I don't have the chem skills necessary for this calculation quite yet.


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## Raul-7 (Feb 4, 2004)

It will raise your kH [CO3/(CO3)2], but in addition it will raise your gH [Ca++, Mg++] aswell.


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## Gumby (Aug 1, 2005)

I am aware of this, and purchased it for this reason. My tapwater has a GH of <1 and a KH of <1. Should work out just right  If only I knew how much to add.


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## Salt (Apr 5, 2005)

I don't like using Dolomite because it adds too much magnesium (in my OPINION). I shoot for a 3:1 to 4:1 ratio of calcium:magnesium. With Dolomite, it's 1:1.65 calcium to magnesium (it actually adds *more* magnesium than calcium). Check out Edward's post in this thread showing what happens to Rotala Wallichii when magnesium levels reach more than 10 ppm.

Regardless, the numbers are (I don't know how many grams per teaspoon, if you don't have a lab balance, get one off ebay! ):

To raise GH by *1 dGH* with dolomite, you would add *31.06 milligrams* per *gallon* of water. (62% from magnesium, 38% from calcium.)

This dose will also raise the alkalinity by half a degree (.49840 dKH increase).

Example: To raise 135 gallons by 1 dKH: 135 gallons * 31.06 milligrams * (1 dKH / .49840 dKH) = 8413.121990 milligrams / 1000 = 8.41 grams. This will raise GH by 2 dGH (1:1.65 calcium:magnesium ratio)

----- Work / Calculations ----

Calcium = 40.078 g/mole

Magnesium = 24.305 g/mole

Carbonate (CO3) = 60.0089 g/mole

Dolomote (CaMg[CO3]2) = 184.4008 g/mole

1 dGH for calcium = 7.14691 ppm

1 dGH for magnesium = 4.33419 ppm

1 dKH for carbonate = 10.7145 ppm

Increase 1 dGH of magnesium & calcium in a locked 1.65:1 mg:ca ratio using dolomite (CaMg[CO3]2):

Calcium = 7.14691 ppm / (40.078 g/mole / 184.4008 g/mole) = 21.73418 mg/Liter

Magnesium = 4.33419 ppm / (24.305 g/mole / 184.4008 g/mole) = 13.18053 mg/Liter

Ratio = 21.73418 / 13.18053 = 1.64896 : 1 (Mg : Ca)

21.73418 mg adds 1 dGH for calcium & 1.64896 dGH for magnesium

21.73418 mg = 2.64896 dGH total

8.20479 mg = 1 dGH (.62249 dGH from Magnesium & .37751 dGH from Calcium)

Converted to Gallons:

8.20479 mg * 3.785412 liters/gallon = 31.05851 mg

For Carbonate:

10.7145 ppm CO3 = 1 dKH

10.7145 ppm / (120.0178 g/mole / 184.4008 g/mole) = 16.46224 mg/Liter

8.20479 mg / 16.46224 mg = 0.49840 dKH


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## Laith (Sep 4, 2004)

And dolomite (or at least the dolomite I tested ages ago) takes about 2 years to dissolve...


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