Participated calcium bicarbonate?

[slicko]

Hi randy, others

Is participated calcium bicarbonate ok to use for calcium suppliment? And if so what sort of mix would be required to be the same strength as using dow flake?

 

[Randy Holmes-Farley]

Not sure what you mean.

Calcium bicarbonate is not a real material. Calcium carbonate (limestone, aragonite, etc.) is not suitable.

I don't know what precipitated calcium bicarbonate would mean.

 

[slicko]

Yes looks like i read the bag wrong it is calcium carbonate so no use to me i will swap for calcium chloride! Thanks randy

 

[Randy Holmes-Farley]

You're welcome.

FWIW, I discuss calcium carbonate as a supplement here:

Chemistry And The Aquarium: Calcium Carbonate As A Supplement ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/issues/july2002/chem.htm

Happy Reefing.

 

[okeydokey]

I know calcium bicarbonate does not exist. [Ca(HCO3)2(s)]

May I/How to formulate calcium bicarbonate solution easily without using Calcium reactor?[Ca(HCO3)2(aq)]

 

[Randy Holmes-Farley]

I know calcium bicarbonate does not exist. [Ca(HCO3)2(s)]

May I/How to formulate calcium bicarbonate solution easily without using Calcium reactor?[Ca(HCO3)2(aq)]

You cannot make any sort of concentrated solution. It will precipitate calcium carbonate. Lower pH helps, which is how a CaCO3/CO2 reactor works. Pressurized CO2 on calcium carbonate can dissolve more, but it is hard to use.

I discuss it here:

http://www.advancedaquarist.com/issues/july2002/chem.htm

from it:

Knowing the KSP and some other constants, it is a textbook calculation to determine how much calcium carbonate can dissolve in pure water in the absence of atmospheric carbon dioxide. Pankow (Aquatic Chemistry Concepts; 1991) carries out this calculation for calcite (a slightly less soluble form of calcium carbonate than aragonite).

For those really interested in the chemical details, this calculation is actually much more complicated than it would first appear (i.e., more complicated than for a simple salt like NaCl). You cannot simply solve equation 3 for [Ca2+] and [CO32+]. You need to take into account the fact that some of the carbonate that comes from dissolution will be converted into bicarbonate (HCO3-) and even carbonic acid (H2CO3). This conversion permits more CaCO3 to dissolve before the carbonate concentration rises too high to dissolve any more. One also needs to take into account the fact that calcium can exist as CaOH+, which effectively lowers the calcium concentration (though not very extensively at pH values below 11).

From this calculation, we find that the solution at equilibrium contains about 6 ppm calcium and 0.3 meq/L alkalinity, and results in a pH of 10.0. If we correct this result for aragonite instead of calcite (which is slightly more soluble), we get about 10 ppm calcium and 0.5 meq/L alkalinity, with a pH of just over 10 (which is what about what I got when I initially dissolved both AragaMIGHT and Southdown aragonite sand in RO/DI water). For comparison, full strength limewater contains about 820 ppm calcium and 41 meq/L alkalinity.

The calculation is even more involved when atmospheric carbon dioxide is allowed to enter the system. Thankfully, Pankow has again done the calculations for us. In equilibrium with normal atmospheric carbon dioxide, the solubility is increased by about a factor of 3, with the alkalinity about 1 meq/L and the calcium about 20 ppm. In this case, the pH drops to about 8.3 as the carbon dioxide enters the system. Confirming Pankow's calculation, this result is about what I got when I let both AragaMIGHT and Southdown aragonite sand sit in RO/DI water for a few days). Still, these calcium and alkalinity values are about 40X lower than for saturated limewater, so are likely not enough to satisfy the needs of most reef tanks.

At one point I had the bright idea of adding aragonite to seltzer (soda water) bought at the grocery store to really boost the solubility and maybe have a nice, liquid additive. Seltzer has far more carbon dioxide in it than water in contact with normal air (which is why it goes flat when open), and that extra carbon dioxide will cause a great deal more calcium carbonate to dissolve (at 3.5 atmospheres CO2, the solution would contain more than 10 meq/L alkalinity and would be similar to limewater in potency, but much lower in pH). If only I had been able to mix them!! Instead, it ended up a science experiment for the kids, with the added aragonite sand providing a perfect surface for the carbon dioxide to turn into the gas phase and erupt from the bottle as a fountain of water, gas, and sand!

 

[okeydokey]

Thank you, Randy

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.