Question

Cory · Mar 8, 2016

How much dkh and calcium does it take to grow 1 gram of sps calcium carbonate?

Maybe this could be a chemiatry question of te day.

JimWelsh · Mar 8, 2016

The molar mass (aka molecular weight) of calcium carbonate is 100.0869. Of that, the calcium portion is 40.078 and the carbonate portion is 60.01, so it takes 0.6 grams of carbonate and 0.4 grams of calcium.

But, from the way you phrased the question, I think you are asking about the amount of depletion of the tank water. If I am correct about what you mean to ask, then you need to specify the volume of the tank water. Do you mean, "How much will alkalinity and calcium go down in a X gallon tank when 1 gram of sps calcium carbonate skeleton is created?"

Cory · Mar 9, 2016

JimWelsh said:
The molar mass (aka molecular weight) of calcium carbonate is 100.0869. Of that, the calcium portion is 40.078 and the carbonate portion is 60.01, so it takes 0.6 grams of carbonate and 0.4 grams of calcium.

But, from the way you phrased the question, I think you are asking about the amount of depletion of the tank water. If I am correct about what you mean to ask, then you need to specify the volume of the tank water. Do you mean, "How much will alkalinity and calcium go down in a X gallon tank when 1 gram of sps calcium carbonate skeleton is created?"

Yes exactly. Lets say in 100 gallons. Do you know in ppm calcium and dkh?

JimWelsh · Mar 9, 2016

That 0.6 grams of carbonate = 0.6 / 60.01 = 0.01 moles of carbonate ions = 10 millimoles * 2 for the divalent charge on the CO3-- ion = 20 meq = 56 dKh of alkalinity, but that is in the context of 100 gallons = 378 liters of water, so the effect on the overall tank water is a reduction of only 56 / 378 = 0.15 dKh.

For calcium, the 0.4 gram reduction in 378 liters is 400 mg / 378 liters = 1.06 PPM calcium.

They are calculated differently because alkalinity is expressed in units that are expressing the amount of charge per liter, which a factor of the number of ions, or molarity, whereas calcium is expressed in PPM, which is a measure of the weight of the substance per liter.

Cory · Mar 9, 2016

So its .15dkh and 1.06ppm calcium to make 1 gram of coral in 100 gallons of water?

JimWelsh · Mar 9, 2016

To make 1 gram of calcium carbonate coral skeleton, yes.

Cory · Mar 9, 2016

Thanks. 1.5dkh then would make 10 grams of coral. I wonder where all my dkh goes to, it definitely isnt into coral lol.

JimWelsh · Mar 9, 2016

Coralline algae on glass and/or rocks? Abiotic precipitation onto heaters, etc.? Does your alkalinity demand match your calcium demand?

Cory · Mar 9, 2016

I dont think my calcium matches my alk. It seems alk drops while calcium climbs. I dont need a heater because of the pumps and lights. I do have corraline growing. Are they skewing the results?