Calcium Reactor CO2 Question

[Randy Holmes-Farley]

After more digestion and my often struggles with chemistry the above is what confuses me and I know I'm being dense but please have patience as I'm trying to grasp the science.

1) Coral skeletons supposedly melt at 7.8 although I believe Reborn is marketed around 7.2. That's confusing.

2) Since nitrification contributes acid then wouldn't that on the surface of the coral skeleton not affect the surface PH and have an affect? Granted there's likely no affect to the system but I'm associating this with acid being placed on our hands and perhaps oversimplifying it and why I can't wrap my mind around the fact that acid produced via bacteria existing on the coral skeleton wouldn't have the affect I'm seeking.

Not looking to see if it's material in nature at this point and more to just understand the process. I know I'm confusing the affects of acid produced from nitrification with the affects of CO2 on PH but I don't know why.

The term melt is nuts. It dissolves, like salt. It would not melt until it reached thousands of degrees.

There is a specific pH where aragonite is exactly at equilibrium with seawater, neither dissolving nor precipitating. It depends on alk and temp and salinity, but is around pH 7.8. At any pH below that level, it can begin to dissolve, and the further you are below it the faster it dissolved and the more it can dissolve.

Calcite is a bit more stable and takes a little lower pH.

Higher surface area materials will tend to dissolve faster at a given pH.

Reactions that produce acid near the bulk water tend to not lower the pH enough to do anything as seawater is pretty strongly buffered against pH changes.

In a reactor, if you add enough CO2 you can overpower the buffering and drive the pH low enough to detect dissolution.

 

[GARRIGA]

There is a specific pH where aragonite is exactly at equilibrium with seawater, neither dissolving nor precipitating. It depends on alk and temp and salinity, but is around pH 7.8. At any pH below that level, it can begin to dissolve, and the further you are below it the faster it dissolved and the more it can dissolve.

Calcite is a bit more stable and takes a little lower pH.

Higher surface area materials will tend to dissolve faster at a given pH.

Melt seems to be a hobby term but I get your point.

Pertaining to surface area then would flow also accelerate the process since water has an eroding effect, therefore, the combination of ph being lower than 7.8 along with higher flow rate against a container being wider vs tall (increasing the surface area being contacted) wouldn’t have a greater ability to dissolve those coral skeletons?

 

[Randy Holmes-Farley]

Melt seems to be a hobby term but I get your point.

Pertaining to surface area then would flow also accelerate the process since water has an eroding effect, therefore, the combination of ph being lower than 7.8 along with higher flow rate against a container being wider vs tall (increasing the surface area being contacted) wouldn’t have a greater ability to dissolve those coral skeletons?

Flow has an effect in that it can bring new lower pH fluid to a CaCO3 surface faster and take away the dissolved Ca++ and CO3-- faster, speeding dissolution, but not due to physical erosion. If the effluent pH doesn't change, then the flow won't have an impact.