Aquatic Plant Forum banner
1 - 2 of 2 Posts

·
Registered
Joined
·
678 Posts
Zapins said:
i would like some help in figuring out how much of each chemical (in grams) to add to my 55 gallon tank to raise the gh to by 1 degree of general hardness (~18ppm) in a 4:1 ratio between the calcium and the magnesium.
I haven't totally figured out czado's methods but he is incorrect. A degree of German Hardness is equivalent to 10 ppm of calcium oxide (CaO) or 17.86 ppm of calcium carbonate (CaCO3). CaO contains 7.1469 ppm of calcium and 2.853 ppm of oxygen. CaCO3 contains 7.1469 ppm of calcium and 10.7145 ppm of carbonate (CO3). See my work below.

To raise gH by 1 dgH in 1 gallon of water using calcium chloride dihydrate and magnesium sulfate heptahydrate while maintainig a 4:1 ratio of calcium to magnesium cations:

- Add 0.07939 grams of CaCl2*2H2O
- Add 0.03328 grams of MgSO4*7H2O

For 55 gallons, this would be 4.37 grams CaCl2*2H2O and 1.83 grams of MgSO4*7H2O.

Use this as a starting point. There are other factors that will affect the actual gH reading - calcium and magnesium cations may not register 100% equally on your test, the quality of the compounds used (agricultural grade from Greg Watson vs. reagent ACS grade from a lab supplier), compounds in your specific water chemistry - so simply adjust the measurement by using the same percent of each. (Example, if it raises it a bit more than you wanted, try multiplying each measurement by .75 to dose at 75% strength next time.)

DO NOT DISSOLVE CaCl2 and MgSO4 IN THE SAME CONTAINER! - The calcium and sulfate ions will bind and calcium sulfate will precipitate out. Calcium Sulfate is "insoluble" - it will dissolve but verrryyy sloowwllly.

-------------------------

Calculations - Assumes an EDTA chelation gH test in which calcium and magnesium cations register equally

- Calcium = 40.078 g/Mole

- CaCl2*2H2O Dihydrous Calcium Chloride = 147.01396 g/Mole

- Magnesium = 24.305 g/Mole

- MgSO4*7H2O Heptahydrate Magnesium Sulfate = 246.47556 g/Mole

1 dGH (Degrees of German Hardness) for calcium = 7.14691 ppm or mg/Liter / 1000
= .00714691 g/Liter / 40.078 g/Mole = .00017832 Moles

1 dGH (Degrees of German Hardness) for magnesium:
.00017832 * 24.305 = .0043342 g/Liter * 1000
= 4.33419 mg/Liter or ppm

Increasing 1 dGH of Calcium (7.14691 ppm) in 1 liter of water using Dihydrous Calcium Chloride:
7.14691 / (40.078 / 147.01396) = 26.21626 mg/Liter

Increasing 1 dGH of Magnesium (4.33419 ppm) in 1 liter of water using Heptahydrate Magnesium Sulfate (Epsom Salt):
4.33419 / (24.305 / 246.47556) = 43.95274 mg/Liter

Converted to Gallons:

Increasing 1 dGH of Calcium in 1 gallon of water using Dihydrous Calcium Chloride:
26.21626 * 3.785412 = 99.23934 mg/Gallon

Increasing 1 dGH of Magnesium in 1 gallon of water using Heptahydrate Magnesium Sulfate (Epsom Salt):
43.95274 * 3.785412 = 166.37924 mg/Gallon

Converted to a 4 : 1 ratio of calcium : magnesium

99.23934 mg/Gallon CaCl2 = 1 dGH
166.37924 mg/Gallon = 1 dGH

79.39147 mg/Gallon = .80 dGH
33.27585 mg/Gallon = .20 dGH
 

·
Registered
Joined
·
678 Posts
Zapins said:
i assume you ment add 4.37 grams CaCl2*2H2O and 1.83 grams of MgSO4*7H2O to raise 55gal by 1 Gh?
Correct

Zapins said:
though if they react in a container wouldnt they just react in my fishtank anyway?
I am not a chemist, this is only my understanding... they don't really "react." The ions just sort of "bump up" against each other in such a small space and make the dissolve time take longer. In a tank, it's much more dilute to cause precipitation.

Zapins said:
should i replace the Gh every week or just wait until water change day?
Totally up to you. Adding the compounds raises GH. If you do a water change and there is little to no GH in your water, then a water change will lower GH.

Be aware that it is possible that your test kit may be bad, especially if it's very old. Always shake the testing reagents before using them. You may want to buy a new GH test kit just to be sure.
 
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top