Why run CO2 instead of carbonic acid ?

[Sherman]

Why we take the trouble to run CO2 through the calcium reactor to melt the media instead of running
any carbonic acid directly to melt the same media


Please share your view

 

[KrisReef]

Because CO2 is cheap and clean and it is highly soluble in seawater?

 

[Sherman]

Because CO2 is cheap and clean and it is highly soluble in seawater?

Thank You Kris

 

[Breadman03]

Because CO2 is cheap and clean and it is highly soluble in seawater?

Agreed, plus readily available in most developed countries from local suppliers and is able to be used with readily available equipment.

 

[Sherman]

Agreed, plus readily available in most developed countries from local suppliers and is able to be used with readily available equipment.

A bit different here in Singapore. Only certain town has such shop.And no all the reefers can afford a car.(A small 1200cc car can cost u S$80K. And you need to get a COE to own a car in Singapore.This COE depend on season can be as high as S$15k. That is initial investment to own a car in Singapore)
Most of us move around taking train or bus.
Its inconvenience carrying a 5 kg bottle moving around with public transport.
That is why I thought if carbonic acid can be use it is lighter and easier to carry around

 

[Elegance Coral]

It's basically the same thing, so you should be able to do it. I'd suggest starting low, checking PH and working your way up.

 

[Sherman]

It's basically the same thing, so you should be able to do it. I'd suggest starting low, checking PH and working your way up.

Thk You Elegance Coral for sharing.
So can also use carbonic acid.
What is the cheapest and easiest available carbonic acid ?

 

[Scrubber_steve]

Thk You Elegance Coral for sharing.
So can also use carbonic acid.
What is the cheapest and easiest available carbonic acid ?

Carbonic acid is just hydrated CO2 .... soda water

 

[Sherman]

Carbonic acid is just hydrated CO2 .... soda water

Hi Scrubber so I can buy ready mix off the shelf or I need to get some powder form and mix myself.

 

[lapin]

Here we have soda water making machines. They have small co2 bottle and you make your own carbonated water. It is very expensive compared to refillable 5kg bottles but maybe something like this can work for you?
https://www.amazon.com/dp/B076X4C6LY/ref=psdc_7956268011_t1_B07DP5941K

I do believe this to be true:
You can't buy carbonic acid because the pure form would rapidly decompose to basically carbonated water. Carbonated water itself contains more carbonic acid than you could possibly keep dissolved at atmospheric pressure, so you'd need to keep the solution pressurised.

 

[Breadman03]

You might be interested in checking out this thread. The poster set up a calcium reactor to run on club soda and appears to be successful with it.

 

[Sherman]

Here we have soda water making machines. They have small co2 bottle and you make your own carbonated water. It is very expensive compared to refillable 5kg bottles but maybe something like this can work for you?
https://www.amazon.com/dp/B076X4C6LY/ref=psdc_7956268011_t1_B07DP5941K

I do believe this to be true:
You can't buy carbonic acid because the pure form would rapidly decompose to basically carbonated water. Carbonated water itself contains more carbonic acid than you could possibly keep dissolved at atmospheric pressure, so you'd need to keep the solution pressurised.

Hi lapin,
Thank You for sharing.

 

[Sherman]

You might be interested in checking out this thread. The poster set up a calcium reactor to run on club soda and appears to be successful with it.

Thank You Breadmano3. I saw it. Look interesting

 

[Randy Holmes-Farley]

Carbonic acid (H2Co3) is just hydrated Co2 (CO2 gas in water). There is no such thing as solid carbonic acid at any reasonable temperature.

You could run soda water through a CaCo3/Co2 reactor, but you get two big problems that make it less than desirable, and I have addressed these before.

The main problem is that calcium carbonate is poorly soluble in freshwater, even at the pH of soda water. Depending on how much you are able to pressurize the Co2 into the water, you will not get anything more potent than limewater, so why not use that and avoid the low pH issues that result? You will be evaporation limited in how much calcium and alk you can supply that way.

Chemistry And The Aquarium: Calcium Carbonate As A Supplement
https://www.advancedaquarist.com/2002/7/chemistry

Here's the relevant section from that article:

Dissolution of CaCO3 in Water Prior to Addition
The best way, in my opinion, to use calcium carbonate as a supplement is to dissolve it in fresh water prior to addition. In this sense, it can be used rather like limewater. One can rig up an automatic evaporation replacement system using appropriate pumps and float switches, and just use water saturated with CaCO3 instead of limewater. Alternatively, one can simply pour the saturated water into the tank each day. Unfortunately, the fact that you can add it this way is a mixed blessing. One reason that you can add it this way is that there is so little present that the carbonate does not drive up the pH too much.

So how much goes into solution? This question is rarely addressed directly, and it is because of one big complication: carbon dioxide from the atmosphere. In the case of limewater, it is partially destroyed by atmospheric carbon dioxide (producing insoluble CaCO3 from the dissolved calcium and hydroxide). In the case of calcium carbonate, however, the solubility is actually increased by mixing with carbon dioxide. The reason that the solubility is increased is that the carbon dioxide enters the water, becomes carbonic acid (equation 1), and largely combines with carbonate ions to form two bicarbonate ions (equation 2):

1. CO2 + H2O ⇔ H2CO3 ⇔ H+ + HCO3-
   
   
2. H+ + CO32- ⇔ 2HCO3-
   

The net effect is that the concentration of carbonate ions declines: since the solubility of calcium carbonate is governed by the multiplication product of the calcium and carbonate concentrations (equation 3), more calcium carbonate can dissolve to regain saturation.

3. KSP = [Ca2+][CO32-]

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!

 

[Randy Holmes-Farley]

The reason that using seawater from the tank instead of freshwater works is because calcium carbonate is MUCH more soluble in seawater than freshwater at the same pH, and because you have no evaporation limit to how much you can run through the reactor each day. :)

 

[Sherman]

Thank You Randy for the detail explanation.