calicium hydroxide question

[untamed]

Originally Posted by rayjay

Kalk replaced calcium used by corals from the water, and, while it will boost pH, especially if added too fast, it does not boost alkalinity.
What it does do though is keep the alkalinity from being used up by kicking the pH a little with each addition.

The way you say that makes it sound like Kalk doesn't deliver Alkalinity to the tank, which it of course does. Kalk is a well known balanced additive..If you add too much, you will certainly raise both Ca and Alk. It think what you are trying to say is that Kalk isn't really a good choice if one needs to raise Alk independently of Calcium because it will drive both. (Although more of a balanced additive is frequently the real solution to low-alk issues)

As a beginning kalk user, I suggest reading this:
http://www.advancedaquarist.com/issues/feb2003/chem.htm

I think this the key statement from the article:

"The calcium ions in the solution obviously supply calcium to the tank, and the hydroxide ions supply alkalinity. Hydroxide itself provides alkalinity (both by definition and as measured with an alkalinity test), but corals consume alkalinity as bicarbonate, not hydroxide. Fortunately, when limewater is used in a reef tank, it quickly combines with atmospheric and in-tank CO2 and bicarbonate to form bicarbonate and carbonate:"