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Re: Carbonate Hardness

Hello Roger,

It seems that we are talking here a bit past each other, probably
because the term "Carbonate Hardness" is often misapplied to mean
"Alkalinity".

If one wants to measure ALKALINITY, then titration is both an easy and
accurate method. Of course it does not tell one where the alkalinity is
coming from, but that is another story. 

In nature, alkalinity _might_ be equal to carbonate hardness, but there
is no guarantee. If baking soda is added to the water, as many aquarists
do, then the two values DEFINITELY will NOT be equal! So that is the
best reason why one should not use the term "Carbonate Hardness" for
"Alkalinity". It is simply wrong.

CARBONATE HARDNESS is just that -- that component of dissolved calcium
and magnesium in water that, as you say it, is counterbalanced by
bicarbonate ion. It is a _component_ of alkalinity. It is also called,
properly, "Temporary Hardness", because it can be removed by boiling. 

If, as you say, the EPA talks about "non-carbonate hardness", then, by
implication, there IS a "carbonate hardness" (perhaps of no interest to
them), and, I am certain, that they do not mean "Alkalinity" by it! 

The example you cite with your water is right: Your water has 1 "degree"
of Carbonate Hardness and 7 "degrees" of Alkalinity. Nothing more,
nothing less. I place "degree" in quotes, because *a priori* one would
not know WHICH "degree" you have in mind -- American, English, French,
German, or ... As you know, the EPA uses milligrams-per-liter (or ppm)
as units for Water Hardness. Wouldn't it be a good idea for aquarists
also to use it, exclusively?

Unless I misunderstood your other example, the boiling method CAN be
used on waters without any Permanent Hardness: The second value
(Permanent Hardness) just will be "zero". Subtracted from Total Hardness
it will give you the correct answer -- all water hardness is due to
Temporary or Carbonate Hardness.

What I had in mind, mentioning "other alkalies" in the water in the SW
US, was borates and silicates. Perhaps my geographical designation was
not accurate enough.

Best,

George



> Date: Tue, 19 Sep 2000 08:02:43 -0600 (MDT)
> From: "Roger S. Miller" <rgrmill at rt66_com>
> Subject: Re: Carbonate Hardness
> 
> On Tue, 19 Sep 2000, George Slusarczuk wrote:
> 
> > There IS a relatively simple way to measure "true" Carbonate Hardness.
> > It is based on the fact, that carbonate hardness equals to "temporary
> > hardness" (that's where the term "carbonate hardness" came from).
> > Measuring Total Hardness and then Permanent Hardness, and then
> > subtracting the second from the first gives one temporary (carbonate)
> > hardness.
> 
> "Carbonate hardness" as you describe it here measures that part of the
> total hardness that is balanced by carbonates.  If the water contains more
> carbonate than general hardness then this method does not measure the
> amount of bicarbonate in solution (which is, after all, what we want to
> measure).
> 
> My tap water for instance, contains about 1 degree of general hardness
> and 7 degrees of alkalinity--all apparently from bicarbonate.  Going
> through the procedure you describe, the water would have 1 dGH before
> boiling (Total Hardness) and 0 dGH after boiling (Permanent Hardness) and
> the method would determine 1 dGH of "carbonate hardness".
> 
> Uh... That's not a very useful result.
> 
> The boiling method works in some water, but not in others.  The tip off
> comes from the measure of Permanent Hardness.  If that is 0 then the
> method can't be used.  As it happens this value often is 0.
> 
> As an aside, the USGS (and EPA, I believe) use the term "non-carbonate
> hardness", but I have found no use in modern English-language
> water-quality literature for the term "carbonate hardness".
> 
> > Of course, many waters might not have any Permanent Hardness or any
> > Carbonate Hardness, but most will probably have a mixture of both.
> > Waters in the South-Western US will probably have a relatively large
> > "other alkalies" component that will add to the _alkalinity_
> > measurement, but NOT to the water hardness value.
> 
> For what it's worth, its very rare for unpolluted natural water from the
> southwest to contain a significant amount of anything that will contribute
> to alkalinity except bicarbonate.  I have seen analyses that contained
> significant amount of HS- and I understand that acetate may be more common
> than is widely recognized.  Either of these could appear as part of the
> measured alkalinity but these are rare in natural water; HS- might appear
> in some oil field brines, but typically both of these flag heavily
> polluted water such as septic tank or landfill leachate and will never
> show up in a public water supply.  These pollutants are probably more
> common outside the southwest US.
> 
> Roger Miller