1.3.2 Testable Parameters: Calcium
Description
This article is from the ReefKeepers FAQ, by several authors (see the Credits section).
1.3.2 Testable Parameters: Calcium
Calcium content is referred to as 'calcium hardness' and is
measured either in parts per million of calcium ion (ppm Ca++) or
parts per million equivalent calcium carbonate (ppm CaCO3).
Calcium hardness is often confused with alkalinity and carbonate
hardness since the 'ppm CaCO3' unit may be used for all three. As
with alkalinity, a calcium level expressed as X ppm CaCO3 does not
imply that X ppm of calcium carbonate is present in the tank; it
merely states that the sample contains an equivalent amount of
calcium as if X ppm of CaCO3 were added to pure water. The
reading also does not tell you how much carbonate is present.
Calcium hardness test kits are different from alkalinity kits.
Some people have reported difficulties with the LaMotte calcium
hardness kit. The Hach 'Total Hardness and Calcium' kit has not
had these reports. Both express results in ppm CaCO3. The
relationship between CaCO3 and Ca++ is:
1 ppm CaCO3 = 0.4 ppm Ca++
The results from a test kit reading in ppm CaCO3 may be converted
to the molar concentration scale by dividing by 100.
100 ppm CaCO3 = 1 mM Ca++
40 ppm Ca++ = 1 mM Ca++
Calcium levels of natural surface seawater are around 420 ppm
Ca++ (10.5 mM). In a well running reef tank you will notice, sometimes
dramatic, calcium depletion. Calcium addition in some form is
essential. A calcium level above 400 ppm is required and a range
of 400-450 ppm Ca++ is recommended. Most reefkeeping books (see
bibliography) explain the options for calcium addition.
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