quick question not realy an emergency

Another interesting debate... feel free to disagree with "the NASA dude"... because we're talking reef stuff, not NASA stuff... on NASA stuff you might be careful... I am no expert in this domain...

My thinking was this... the calcium carbonate in the limestone will have a reaction with the water.... might that be a "variable" that would make harder to control the overall chemistry of the tank?? Since we are dosing for calcium, alk, magnesium, etc, if you introduce something that is altering it at an unknown rate and changing rate, it might make keeping stability harder.

I look at live rock as porous bateria factories to eat nitrates, not as buffers.

Just my opinion.

Mark

 

They're both.

The chemical reaction is pretty straight forward. Calcium Carbonate is soluble in water, as are many things, like salt.

But everything has a limit, and eventually a solution will become saturated.

pH plays the biggest role in the solubility of CaCO3 in water.

Very acidic water can holds lots of CaCO3 in solution.

As the pH goes down (water becomes more acidic) the CaCO3 will dissolve and raise the pH.

As the pH goes up the solubility of CaCO3 goes down.

Eventually you hit an equilibrium.

If the CaCO3 is depleted by corals and other inverts the pH will go down and more will be drawn from the live rock and aragonite sand.

If you artificially raise the pH with a strong enough base the solubility of CaCO3 will lower and you'll form a precipitation of calcium and CO2 from the water. As the CaCO3 precipitates out the pH slowly lowers and the process balances.



There was a recent thread where the user had cloudy water and this is likely what was causing it. Precipitate is in the form of molecule sized small bits of calcium, so it suspends very well in the water, but will eventually settle. All kinds of things can raise pH but in a tank I would look at ammonia from fish waste and hydroxides from the addition of more salt. Lights and plants can also cause pH to raise.

 

IMO, there's really no drawback or affect of water parameters. We all use carbonate based rock and when you add alkalinity supplements, all you are doing is buffering the water against acids. The reaction will be very slow and minute at the PH most reefs tanks are kept at, it's not until the water becomes more acidic that the reactions picks up pace.

 

Definitely not. The live and base rock that people have and buy is all a variety of calcium carbonate. The only difference is source. Calcium carbonate is in natural geologic deposits in the ground, under water, from ancient coral reefs (which is actually where around 85% of the land deposits originated) either on ground or in the water, and you can even create it chemically in a tank yourself (which nobody actually does for their live rock, but it is definitely possible as it is guaranteed to happen if either your Alk or Calcium go too high when you're running a tank. This is the substance that makes up the snow that ensues in those conditions.).

With source comes the issue of pollutants and contaminants. Almost all limestone has some level of phosphates in it. Some has magnesium (a definite bonus for reef keeping). It really depends on the particular deposit's history and characteristics. A lot of research has to go into buying limestone if you want to buy it by cutting out the middlemen of aquarium distributors.
You would want an aragonite variety. It's better at dosing your tank with pH, Alk and Calcium, which is a good thing. Note that many people use "Aragonite Sand" for DSB, Calcium reactors and DT sand bed purposes. It's the same crystalline form of CaCo3 in limestone as in the sand.
You want to make sure it's a low phosphate variety that doesn't contain copper and has a low phosphate level (all limestone will have it). There shouldn't be too much else to be concerned about in terms of contaminants from its formation, but sitting out exposed to air and rain is a wild card I'm not even gonna touch. Likely, any distributor closer enough the the mining company in the supply chain should have the information you'd need to make the best decision.

Funny enough, that's the exact time you'd want to dose Kalk to raise your pH, Alk and Calcium all in one fell swoop...

As a side note, as I was researching the above information on limestone, I discovered that the live rock in my aquarium, which is mined from the south Florida area then aquacultured into live rock, is actually mostly brain and Elkhorn coral skeletons. It makes sense, given its highly dense, solid-block nature.

 

Great posts and explanations.... I have learned a lot in this thread.

Thanks
M

 

I was also thinking of pollutants as other materials that could have been formed in with the limestone, as well as pollutants potentially added during the quarrying/storage/delivery process.
Is there any way to be sure your slab of limestone is 100% calcium carbonate? I don't know so I'm just asking if anyone knows for sure.

Even very small amounts of things like copper can have very negative effects especially over time (maybe even years) if they're allowed to build up in the system.

 

The impression I got when I was looking all that stuff up was that the people running quarries tend to have a good idea of the contents of the stone, as a lot of research goes into a mining operation before they even consider opening up shop. On some of the types of limestone on Wikipedia they even list a couple as having a high phosphate content.

It's definitely something to do a lot of research into with the suppliers, but it's not like generic limestone is particularly harmful barring the presence of a couple trace minerals. Especially considering that copper, or any other element that would harm a reef tank, would kill the actual corals that make limestone, I really wouldn't be enormously concerned about anything other than phosphates in the limestone.

Limestone is a sedimentary rock, so it's only made by being deposited by something. In fact, it's closer in its formation method to coal than it is to granite or to slate.