Calcium, DKH, and Magnesium

[Jeremy Lain]

Can someone please help me understand what Calcium, DKH, and Magnesium are doing to form coralline algae?

 

[Chuk]

they don't form the algae. The algae takes the minerals from the water to create a kind of skeleton as it grows and encrusts/ plates pretty much just like a coral.

 

[Jeremy Lain]

Alright. Can someone please post a diagram of what is happening?

 

[Chuk]

well the Ca and Alk are simple its basically the Ca++ ions in the water combines with the bicarbonate ions HCO3- of alkalinity to form calcium carbonate CaCO3. Magnesium is a little trickier if I remember correctly it forms carbonate structures as well either magnesium bicarbonate MgHCO3 or magnesium carbonate MgCO3. I think I saw an article by Randy Holmes Farley about magnesium in seawater one time way back when. I will see if I can track it down again.

 

[Chuk]

http://reefkeeping.com/issues/2006-06/rhf/index.php

https://www.advancedaquarist.com/2003/10/chemistry

Found it. There's more than this too but its a start.

 

[Randy Holmes-Farley Verified Community Expert]

Alright. Can someone please post a diagram of what is happening?

I can't see how a diagram can explain it especially well, but....

Coralline aglae is an organism just like corals or green hair algae. It grows by encrusting rocks and other surfaces.

It needs many things from the water to live, including substantial amounts of calcium, alkalinity, and magnesium, which it deposits as calcium carbonate. In the case of coralline, the crystalline form of calcium carbonate is called high-Mg calcite, and it uses somewhat more magnesium than most corals, per unit of alk and calcium consumed.