[mike77]

Kalk "Must Reads"

For those that are new to the topic, here are a couple of valuable links to articles by Randy Holmes-Farley:

http://www.reefkeeping.com/issues/2003-05/rhf/feature/index.php
Degradation of Limewater in air. It gives a lot of information on testing the solution, since the topic is necessary to understand before conclusions about degradation can be formed. It is also very reassuring about non-reactor methods of kalk prep and storage for dosing.

http://www.reefkeeping.com/issues/2005-01/rhf/index.php
What Your Grandmother Never Told You About Lime

Mike77

 

[mike77]

pH for testing Kalk-You might drive yourself crazy...

[Snip] You can also test the effluent's pH, although this method is less effective.

Here is an excerpt from another RHF article. It backs your point on the use of pH for testing Kalk. A decrease of 0.2 pH units would equate to a 37% drop in saturation. If my memory is correct, typical pH meters are +/- 0.2 --the reproducibility is not accurate enough for this task, and you could go crazy chasing phantom problems by using pH to test kalk.

Quote: For certain kinds of pH measurements, direct comparison to a known standard may be more useful than using the absolute readings that the pH meter shows. For example, to assess the strength of limewater via pH, make a standard of known saturated limewater (from, for example, a teaspoon of calcium hydroxide in a cup of pure fresh water). That solution has a pH of about 12.45 at 25ºC, but regardless of what is measured, use the number as the standard and see how far off from actual limewater it is (if it is 0.1 pH unit lower, then the limewater is about 79% saturated; 0.2 pH units lower and it is 63% saturated; 0.3 pH units lower and it is about 50% saturated; 0.4 pH units lower and it is 40% saturated, etc.). In this case, exact temperature equivalence between the samples is important. A difference of only 3ºC means a pH difference of 0.1 pH unit for saturated limewater.
End Quote.

Mike77