High Tide Aquatics

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A_Lee

A_Lee

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Normally, reading advanced aquarist magazine online clears things up, but now I am just confused out of my mind.
We all know stony corals use calcium and carbonate to grow.
I'm assuming when we use the term carbonates, we are referring to both CO3--, and HCO3 right?


How exactly do corals utilize it though? Do they take calcium and carbonate, and use them separately, or actively combine them to form CACO3, and then use it? Are calcium and carbonates used in a certain ratio?
What affect does carbonate have on our corals exactly?
Do stony corals take up calcium and carbonate ions in certain proportions? And what role does Magnesium play in all this?
CO3-- and HCO3 ... when we test for dKH, are we testing for both of these or only CO3--?

And now the big question. What EXACTLY is alkalinity? I've read in some places the term alkalinity is not synonymous to dKH.
What difference is there?

Sorry many questions but I am sure many of us could use clarification on the above :p
 
Someone more chemistry knowledgeable please correct me if I'm wrong, but I'll take a stab at it...

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
Normally, reading advanced aquarist magazine online clears things up, but now I am just confused out of my mind.
We all know stony corals use calcium and carbonate to grow.
I'm assuming when we use the term carbonates, we are referring to both CO3--, and HCO3 right?
[/quote]

That's right. Alkalinity in our hobby refers to carbonate alkalinity, which is the concentration of carbonate and bicarbonate anions in a solution.

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
How exactly do corals utilize it though? Do they take calcium and carbonate, and use them separately, or actively combine them to form CACO3, and then use it? Are calcium and carbonates used in a certain ratio?
...
Do stony corals take up calcium and carbonate ions in certain proportions?
[/quote]

They deposit it as a calcium carbonate skeleton. Because a calcium carbonate molecule is formed from one calcium ion and one carbonate ion, those ions always get used in the same ratio.

That's why it's extremely important to replace alk and calcium using a balanced method. Two part solutions are balanced (one part has alk, the other has calcium). Kalkwasser is balanced because lime has the same balance of calcium and alk. Calcium reactors are balanced because they work by dissolving calcium carbonate.

Things that are NOT balanced are stand-alone calcium or alk/buffer products. You should never use those for regular replenishment of calcium or alkalinity.

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
What affect does carbonate have on our corals exactly?
[/quote]

It's used by the coral as a building block for the coral's skeleton. It's important to note that as corals use carbonate, carbonate alkalinity in the water decreases. When the alkalinity becomes too low the coral will be unable to continue forming its calcium carbonate skeleton. The water will also not be buffered against pH drops. When pH gets low enough the water can actually dissolve the coral skeleton. That's why it's important to replace calcium and carbonate in our tanks!

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
And what role does Magnesium play in all this?
[/quote]

In our tanks, calcium and carbonate are supersaturated. That means that if nothing stops it, it will precipitate out of solution and be unavailable for our corals. Magnesium interferes with this precipitation and helps keep the levels of calcium and alkalinity high. One of the most obvious signs of low magnesium is that even when adding more calcium and alkalinity, the levels of those in the tank do not rise.

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
CO3-- and HCO3 ... when we test for dKH, are we testing for both of these or only CO3--?
[/quote]

We're testing for both. They are readily (and continuously) converted from one to the other. For that reason it doesn't matter if you add carbonate or bicarbonate to your tank, except for the temporary effect it has on pH.

[quote author=A_Lee link=topic=5689.msg71248#msg71248 date=1230063828]
And now the big question. What EXACTLY is alkalinity? I've read in some places the term alkalinity is not synonymous to dKH.
What difference is there?
[/quote]

As I mentioned above, alkalinity is a measure of the concentration of carbonate and bicarbonate ions in solution. This concentration can be expressed in one of several different units: dKH (degrees of carbonate hardness), ppm (parts per million), and meq/L (milliequivalents per liter). These are just different scales (like Fahrenheit vs Celsius) and a value in one scale can be easily converted to a value in another.

I hope that helps!
 
Sweet! That actually helps a ton, thanks!
Okay, so let me ask you this now:
I just added two part to a bucket of pre-mixed salt water. After adding the second part, I saw a white precipitate form ... I am assuming this is CACO3? Will it dissolve back into solution? I also took a pH reading, and it is at or slightly above 8.8 :(
I am experimenting and trying to find out how much two part I need to add to 4g premixed water to get the desired calcium and alkalinity. I guess if this 4g is messed up, I will mix another 4g and try starting with smaller increments of two part. I am thinking pre mix another 4g of water; add 1ml of part one, and 1ml of part two; test; if the desired level is reached, then I know how much I need to add from now on. If the water is not at desirable levels, then repeat.
Does this sound okay?
 
Anthony,

Bulk Reef Supply has a calculator on their website that can help you calculate for two part solutions.

http://www.bulkreefsupply.com/i6/Calcium-and-Alkalinity-Calculator./information.html

Hope this helps.
 
Yeah, what Mike said. This is a good calculator too: http://jdieck1.home.comcast.net/~jdieck1/chemcalc.html

Once calcium carbonate has precipitated out it won't go back into solution. (unless your substantially lower the pH, like in a calcium reactor)
 
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