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Re: Aquatic Plants Digest V4 #556

Hello Dave,

Not that I disagree with the definitions you presented, but I would like
to enlarge some concepts and add a few explanatory comments that might
make the entire subject of Water Hardness clearer (or more confusing).

> On the subject of hardness, I have uncovered and tried to define > the following terms:
>    Hardness:            Ca+Mg

Iron and aluminum ions also add to water hardness, but they are normally
present in much lower concentrations, so their influence on water
hardness is usually nil.

>    General Hardness:    Soap killing (tested by titration with  > "standard" soap solution)

The term "General Hardness" is a translation artifact, similar to that
of "lead as plant nutrient" discussed recently on these pages.

The translator(s) being neither chemists nor aquarists, were faced with
translating the German word "Gesamthaerte" and its abbreviation "GH".
"Gesamthaerte" means "Total Hardness" in German. Not knowing the English
term "Total Hardness" and trying to find something that would fit the
abbreviation "GH", the translators created the term "General Hardness",
which is meaningless. It stuck.

It is interesting, that (as far as I know) the first English-language
book on "Aquarium Water Chemistry" was a translation from German of a
book by Rolf Geisler, published by TFH in 1963. It has the correct terms
"Total Hardness" and "Carbonate Hardness". (It has other serious
translation errors, which is another story.)

So, "General Hardness" is a misnomer for "Total Hardness". It would be
good if the term disappeared from general use, but I don't think that
this will happen: Too few people know the facts.

>    Permanent hardness:  General hardness after boiling the water

Correct. That is water hardness produced by salts of calcium and
magnesium OTHER than carbonates and bicarbonates.

>    Temporary hardness:  General hardness - Permanent hardness

Correct. That is water hardness produced by carbonates and bicarbonates
of calcium and magnesium.

>    Carbonate content:   Total CO3-- (and relatives) content

>    Alkalinity:          Resistance to titration with an acid

An interesting definition! What is actually measured is the amount of
cations counterbalanced by anions of weak acids (like carbonic acid)

>    Carbonate hardness:  Minimum of Hardness and Carbonate content (per Slusarczuk)

I would rephrase that definition :-).
Carbonate Hardness = Temporary Hardness = Water Hardness produced by
carbonates and bicarbonates of calcium and magnesium = Total Hardness -
Permanent Hardness.

>    KH:                  German for carbonate hardness?

Yes -- Abbreviation for "Karbonathaerte"

>    Non-carbonate hardness:   General hardness - Carbonate hardness????

Right. It is the same as "Permanent Hardness" = water hardness produced
by salts of calcium and magnesium OTHER THAN carbonates and
bicarbonates, i.e. sulfates, chlorides, etc.
> Does anyone disagree with any of these definitions????