Reef Chemistry Question of the Day #110 Dolomite

Randy Holmes-Farley · Mar 13, 2015

[h=3][/h]Reef Chemistry Question of the Day #110

When added to a calcium carbonate/carbon dioxide reactor, dolomite can be a suitable way to maintain existing magnesium levels. It is not, however, a suitable way to raise low magnesium levels. Which of the following is the primary reason it is not suitable for substantially raising magnesium?

A. Because it is too slow to dissolve
B. Because it adds to much sulfate to the water
C. Because it adds too much alkalinity to the water
D. Because it is too fast to dissolve

Good luck!

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beaslbob · Mar 13, 2015

C
(adding characters to get more than 3 for post)

fuzzone99 · Mar 20, 2015

Guessing...C

Randy Holmes-Farley · Mar 23, 2015

And the answer is...C. Because it adds too much alkalinity to the water

If you use dolomite to boost magnesium, it is basically dissolving magnesium carbonate (and some calcium carbonate, but we can ignore that for purposes of this question).

When magnesium carbonate dissolves, it releases one magnesium for one carbonate ion.

MgCO₃ → Mg²⁺ + CO₃^2-

That means that for a 100 ppm rise in magnesium, alkalinity will necessarily rise by 23 dKH (8.2 meq/L)

This has more:

http://www.advancedaquarist.com/issues/oct2003/chem.htm

Jmcdaniel0 · Mar 23, 2015

Randy, i really enjoy your posts. Having a BS in Organic Chemistry, I really enjoy reading through your articles. You give just enough detail in the science to make it interesting, but it's not overwhelming for the laymen.

Just thought ide toss that out there