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Re: Carbonate Hardness (was APD V4 #551

Hello George,

You are, of course, right that measurement of alkalinity (the so-called
KH) in many cases does NOT measure "carbonate hardness" -- if other
alkalinity components are present in the sample and thus introduce an

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)

To get a measure of Permanent Hardness" -- measure water hardness on the
original sample. Then boil another water sample gently for about 15
minutes, cool it without exposure to the atmosphere (so that CO2 does
not get reabsorbed), filter out (or let settle out) any precipitated
calcium carbonate and measure hardness again. Your second measurement
will be of Permanent Hardness.

The difference between the initial reading and that done on the boiled
sample IS "temporary" or "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.



> Date: Mon, 18 Sep 2000 08:52:50 -0600 (MDT)
> From: George Booth <booth at lvld_agilent.com>
> Subject: Re: Minor technical corrections
> >Date: Sat, 16 Sep 2000 13:47:49 -0700
> >From: Wright Huntley <huntley1 at home_com>
> >Subject: pH hogwash?
> >
> >4 ) pH is a useful thing to measure, along with alkalinity (unfortunately
> >confused with hardness by calling it "carbonate hardness") primarily to use
> >the CO2 concentration equations or charts to set the CO2 level for proper
> >plant nutrition.
> Just to be perfectly clear: The pH/CO2 charts are based on the measure of the
> carbonate ions present in the water, often called carbonate hardness or KH. KH
> can NOT be measured directly, so an alkalinity test is usually substituted. If
> carbonates are the main form of alkalinity, this will produce useful results. If
> other forms of alkalinity are also present (such as phosphates), the results
> will be garbage.
> >Date: Sun, 17 Sep 2000 11:44:03 -0700
> >From: "Dixon, Steven T. (BEn)" <stdixon at ben_bechtel.com>
> >Subject: CO2
> >
> >Julius Odian wrote:  "[lowering pH with CO2 is bad]"
> >
> >Let's look at the implications of Julius' first sentence.  The equilibrium
> >level of dissolved CO2 in a water column exposed to air is fairly low,
> >around 2 - 3 ppm CO2.
> The theoretical equilibrium value is roughly 0.5 mg/l, +/- some based on
> temperature and altitude. Typical values seen in a non-CO2-injected aquariums is
> 2-3 mg/l due to CO2 generated by the bioload present.
> George Booth
> Keeping those myths from getting out of control