CaCO3 & pH: Questions I Was Never Asked

[Biollante]

Hi,

In answer to questions I was never asked. Being a busy body I can’t help wanting a crack at it…

The whole thing seems to be around KH and coral.

1. How does adding Coral sand (Calcium carbonate) cause pH go up in a freshwater tank? Given that Calcium carbonate doesn't contain any Hydroxyl ions as bicarbonate of soda does.
2. Floating around there seems to be some confusion as to what Coral sand is and should it actually be crushed Aragonite crystals; would that explain the pH rise as it is erroneously thought this contains Hydrogen ions.

First “pH” as I (mis?)understand it.
I have heard many explanations for what pH stands for;

• I will stick with “p” being a mathematical symbol for a negative log function and “H” being the chemical symbol for Hydrogen;
• pH=-log [H+]; to chemists and such like folk these “[]” square bracket thingies indicate concentration.
• For those demanding more precision, pH is the negative logarithm of the hydrogen ion concentration: pH= log 1/ [H+= −log [H+]] (had to look that up.)

The ratio of hydroxyl ion [OH-] and hydrogen ion [H+] concentrations determines pH.

• Therefore even though pH is by definition a (selective) measure of Hydrogen ion activity, it is actually a measure acidity and alkalinity.

Acids give up (donate) hydrogen ions, bases take (accept) hydrogen ions.

Crushed coral is Calcium carbonate, CaCO3. Calcium carbonate occurs naturally in its crystal form in three polymorphs or trimorphs,

1. the most abundant and stable form, the trigonal (bar 3 2/m) symmetry, Calcite,
2. the abundant but somewhat less stable orthorhombic (2/m 2/m 2/m) symmetry Argonite
3. and the rare hexagonal (6/m 2/m 2/m) symmetry, Vaterite.

Calcite, Aragonite or Vaterite it is all CaCO3.

In a sense it is a trick question, since Calcium carbonate in any form will only dissolve easily in acidic or less alkaline water, up to around pH 8.5-8.8. As an acceptor of electrons it “buffers” the water, reducing the acid content, raising the pH or preventing it from falling.

Biollante

 

[DaBub]

Once upon a time didn't you tell Tug something different about Calcium and pH?

Just to be clear, what trick is the trick, in the "trick" question?

Thought you would slide by you big green Santa?

 

[Biollante]

I Have You Down For a Lump of Coal Next Christmas

Hi DaBub,

I don’t recall the “Tug” thing… Something with Calcium, GH and KH…

The “trick” my dear barefooted little pilgrim, is in the premise of the question that ignores the inverse relationship between hydrogen and hydroxyl ions inherent as the hydrogen concentration in solution decreases by adsorption by cations such as calcium, the concentration of hydroxyl ions increase simultaneously.

I do not know who said it first, “GH, KH and pH make up the Bermuda triangle of freshwater aquaria," but I like it.

Biollante

 

[Left C]

What would happen to adding pressurized CO2 to an aragonite substrate in one planted aquarium and adding pressurized CO2 to a dolomite substrate in another planted aquarium ? Both aquariums would be planted with Vals, Anubias, Ferns, etc. and adding a moderate level of pressurized CO2 around 15 ppm ± 5 ppm plus ferts. Also doing weekly or biweekly water changes. ??? Would this be a disaster? How would you set up a stable planted African cichlid aquarium with fish from Lake Tanganyika with pressurized CO2?

 

[Tom Barr]

I just stick with actual CO2 ppm.
This moves around a lot all day and night long.

So how would that influence the KH and does adding an acid like CO2 to water at say a KH or 10 soften the water?
In other words, does adding CO2 cause the KH to shift to CO2 and consumes the KH?

that's what quite a few people have claimed, but I've not been able to destroy KH this way.
If I added say HNO3, I do.

Vinegar, acetic acid will as well, add this to CaCO3 rock and you will see foaming(CO2 released).

The question, "which acid added will do this". This causes even more confusion.
As Aquarist, we can add these different acids to see how they affect KH over time.
Do they remove KH or not?

That is something we can measure.
I think this is more useful than reading in some cases.
Good old experiments to illustrate what is going on specifically.

Regards,
Tom Barr

 

[Biollante]

No Problem

Hi Left C,

Absolute agreement with Tom Barr, experimenting, then beyond that replicating situations we read or hear about, on a small scale (modeling) and observing. You will take a lot of crap from the intelligentsia around here, but you will save a lot of time, money and heartache.

{Additional Disclaimer.}
Generally Lake Tanganyika, pH runs from 7.8 - 9.0. My direct experience is with Cichlids from Lake Malawi that.7.4 - 8.6 and I do not have any understanding of those critters that reside in the over pH 9.0.

Depending on local tap water a pH of 8.2-8.5 seems reasonable.

In these pH ranges Dolomite, Argonite, Calcite and so on are going to have little to no effect whatever.:gw

I use Dolomite as a cap in tanks at much lower pH with 35-40-ppm CO2 and no loss of Dolomite, I can see.

I think you should be just fine.

Biollante