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sterlruth
03/01/2006, 05:03 PM
I have the Lamotte Test kit which measures Calcium in ppm of CaCo3 and would like to know how to convert that to ppm of Calcium.

-Steve

Randy Holmes-Farley
03/01/2006, 07:16 PM
100 ppm CaCO3 equivalents = 40 ppm claicum ion.

This article shows that:

The Units of Measure of Reefkeeping
http://reefkeeping.com/issues/2005-08/rhf/index.php

from it:

"ppm calcium carbonate equivalents

ppm calcium carbonate (CaCO3) equivalents is an ambiguous unit used for a variety of measures by reef aquarists, including alkalinity, calcium, magnesium and total hardness. In the case of alkalinity and calcium, the unit refers to the amount (in ppm) of calcium carbonate that would have to dissolve into pure water to give the same calcium concentration or alkalinity (even if that would be impossible to accomplish). For calcium, 1000 ppm calcium carbonate equivalents equals 400 ppm calcium ion. For alkalinity, 100 ppm calcium carbonate equivalents equals 2 meq/L or 5.6 dKH. In the case of magnesium, the concentration refers to the amount of calcium carbonate that would have to dissolve to provide the same number of calcium ions as magnesium ions are present. For magnesium, 1000 ppm calcium carbonate equivalents equals 243 ppm magnesium ion. In the case of total hardness, the unit refers to the amount of calcium carbonate that would have to dissolve to provide the same number of calcium ions as the total of calcium and magnesium in solution. Using ppm calcium carbonate equivalents for magnesium and total hardness is poor practice as they are hard for most aquarists to understand, but they are used for historical reasons by certain testing companies (e.g., Hach, Figure 3). A calculator for converting between different alkalinity units is online here. A calculator for determining how much of different supplements to add to boost alkalinity, as well as calcium and magnesium, is online here."