Which Magnesium recipe do you use?

[Guest Aurora]

BTW...here's a excerp from a huge post on Reefcentral on Mg, Alk, and Ca by a biochemist....

 

Just a couple of comments on magnesium as I'm not sure these questions were completely addressed (appologies if I missed it).

 

Magnesium is important in a conversation like this because it forms ion pairs with carbonate in sea water (and bicarbonate). Calcium carbonate is substantially supersaturated in sea water (on the order of 300 - 400% typically) and we can easily raise that to 600%+ by maintaining higher alkalinity in captivity. We'd predict that calcium carbonate should spontaneously precipitate, since there's way more of it dissolved in the water than there "should" be. However, that's not what happens. One of the reasons is that magnesium forms those ion pairs with carbonate, making it more difficult for calcium carbonate (solid) to form and precipitate. In addition, magnesium carbonate tends to precipitate out with calcium carbonte during abiotic precipitation. Magnesium carbonate doesn't fit into the crystalline structure of calcium carbonate (whether that is CaCO3 as aragonite, calcite, or even amorphous CaCO3). That tends to discourage further precipitation. So, magnesium really gets in the way of calcium carbonate precipitation and allows CaCO3 to remain supersaturated.

 

Magnesium is extremly abundant in sea water. Yes, Mg is an imporant nutrient for any cell, but cells use so little Mg in their normal biology that it is essentially a drop in the ocean. Magnesium does also precipitate with calcium carbonate though, and calcifying organisms like corals, coralline algae, etc. consume it (just like they consume calcium). However, corals, which produce aragonite, consume Mg very, very slowly. Corals consume about 19 moles Ca for every 1 mol Mg. Magnesium is also about 3 times as concentrated as calcium in normal sea water. Thus, the Mg is 3X the conc. of Ca and gets used by corals at ~1/19th the rate. Very modest replenishment of Mg will easily replace what is lost to coral calcification.

 

On the other hand, coralline algae produce high magnesium calcite. This is a structurally different form of calcium/magnesium carbonate as compared to aragonite, it is more soluble, and has much more Mg. Typically coralline algae have Ca:Mg stoichiometry in the neighborhood of 4:1, not 19:1 as with corals. Coralline algae consume Mg proportionally much faster than corals, though coralline algae also tend to calcify a lot slower than corals. A lot of coralline algae growth can consume a fair amount of Mg, however.

 

Some salts do tend to be deficient in Mg as well, leading to problems from the get-go.

 

Recent evidence suggests that strontium is probably incorporated into the skeletons of calicifying organisms (as is lead, uranium, cadmium, etc.) simply as an impurity. The organisms are not necessarily going to any effert to put these into the skeletons--they end up there just because they get precipitated along with everything else. Magnesium, no the other hand, has very particular distribution patterns in coral skeletons, so it looks like the corals might really be "doing" something with the Mg, though nobody has a clue what that something might be.

 

Chris

http://www.reefcentral.com/forums/showthre...hreadid=1179702

[lanman]

Good information! Thanks!

 

bob

[jnguyen4007]

Yeah, I'll say. That is great information. Thank you.

 

James