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Re: Hardness and Calcium confusion



Hello Frank,

Hate to continue this thread, but must correct a misunderstanding:

Water hardness IS the calcium/magnesium content of water. Pure and
simple. Traditionally it is expressed as milligrams of CaCO3/Liter. For
simplicity in analysis and calculations magnesium is treated as if it
were calcium. Other polyvalent cations DO contribute to hardness, but in
"normal" waters they are insignificant and again are either neglected or
treated as if they were calcium.

Carbonate/bicarbonate is just a counterion to calcium/magnesium cations.
It is the most prevalent anion in "normal" natural waters. But instead
of carbonate/bicarbonate it could be sulfate, chloride or any other
anion, whose salt with calcium/magnesium is soluble. Substituting
another anion for carbonate would NOT change the water hardness at all.

Carbonic acid (H2CO3) is a weak acid and thus forms a good buffer with
calcium/magnesium. Because the carbonates of calcium/magnesium are
practically insoluble (solubility is on the order of 15 ppm for calcium,
slightly more for magnesium) so it is the more soluble bicarbonates
(HCO3-) that form the buffer in "normal" waters and constitute the
ALKALINITY of that water. Some chemistry-challenged people call
alkalinity "carbonate hardness" implying with that name that it has
something to do with water hardness. Aside from historical roots in the
mid-19th century, alkalinity has NOTHING to do with water hardness.
Alkalinity is just a measure of the amount of a strong acid necessary to
drop the pH of the water to an agreed upon value, i.e. color change of
methyl orange indicator (pH about 4.0). Again, for historical and
convenience's sake, the result is expressed as if the alkalinity were
all due to calcium carbonate, i.e. in milligrams/Liter of CaCO3 -- units
identical to those that water hardness is measured in, which
tremendously ads to the confusion!!!

Another confusion about water hardness are the curerently available
"water hardness meters". Some versions are calibrated as "total
dissolved solids meters". They DO NOT measure water hardness, nor
dissolved solids, only CONDUCTIVITY of that water. There MIGHT be a
relationship, but that is another topic.

Let me summarise: Water hardness = calcium/magnesium content.
Alkalinity ("carbonate hardness") = amount of acid needed to lower the
pH to about 4.0, expressed as mg/L CaCO3.

Best,

George



YoHoHo at aol_com wrote:
> 
> I believe the problem is a simple misunderstanding.  The issue of calcium and
> hardness seems to have become one and the same, and of course, they are not.
> There is NO calcium in baking soda, but it does raise the HARDNESS.  Hardness
> is a property that is "made up" or "composed" of a number of materials.  The
> element  calcium, Ca can be one of the contributing materials, but not
> necessary.  Magnesium and several others contribute to "hardness".  The
> baking soda contribution to hardness is from the carbonate, CO3.  (Actually
> bicarbonate, HCO3, in this case, but that will probably confuse the issue
> further, sorry).  Just passing this on in an attempt to clarify, so please
> don't get too worked up.
> 
> I have been reading this thread with interest, as I now have some daphnia and
> moina, and would like to ensure their continued life, and hopefully growth.
> What is a brief synopsis of the tried and sure method to raise them in the
> house.  I have no barrel or tank in the yard, at least not yet (working up to
> it).
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