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Re: Aquatic Plants Digest V3 #328

George Slusarczuk. wrote:


> In response to the
> post on hardness I received a nice letter that, among other things,
> informed me that "for the sake of simplicity" the AGA policy defines
> "alkalinity" as "carbonate hardness"!
> So, how can things change for the better, if erroneous information is
> codified by one part of the hobby?

I wasn't aware that AGA had policies for such things.  Regardless, this is
a very old thread in this group and I believe that those participating in
the discussions all finally agreed that the "carbonate hardness" test kits
actually test alkalinity.  I think George said as much in his own letter
of a few days ago.

In that letter George equated carbonate hardness with temporary hardness,
I'm a little curious about the origin of that definition.  I searched my
volume of "Methods for determination of inorganic substances in water and
fluvial sediments" (U.S. Geological Survey analytical methods manual)  and
found no reference to carbonate hardness.  I then went on to search other
volumes I had on hand that were based on EPA and AWWA methodology and
again found no definitive references to carbonate hardness.  I also
searched my recollection of papers and regulatory documents I've read from
the US and other English-speaking countries and I can't recall any
definitive reference to carbonate hardness.  My search isn't exhaustive,
but as near as I can tell, "carbonate hardness" is not a term used outside
the aquarium hobby in any English-speaking country.  Noncarbonate
hardness, on the other hand, is well defined.

Certainly if we were to accept Mr. Slusarczuk's definition of carbonate
hardness=temporary hardness, then it would not be the same as alkalinity.
My tap water, for instance has 2 degrees of temporary hardness, but 7
degrees of alkalinity.  If I mix a solution of sodium bicarbonate and test
it, I find no temporary hardness, but plenty of alkalinity.

As aquarists we really have no particular interest in temporary hardness,
but we do have a substantial interest in alkalinity.  Temporary hardness
just gives us a breakdown of total hardness and for our purposes I think
we only need to know about total hardness.  If I were a boiler operator
instead of an aquarium keeper then I would care about the breakdown, but
I'm not a boiler operator.

We use alkalinity tests (often sold as carbonate hardness tests) to
measure buffer capacity and to approximate the bicarbonate concentration
used in CO2 determinations. The alkalinity test is a direct measure for
buffer capacity.  Temporary hardness has no inherent relation to
buffer capacity.  An alkalinity test is an excellent measure of
bicarbonate in most unpolluted natural waters.  We can have problems using
it in aquariums because of the contributions to alkalinity from
phosphate, EDTA and a host of other organic acids.  However, you don't
have to do a lot of figuring to figure out that the contribution from
these alternative sources will generally be too small to be an immediate
concern.  And of course, temporary hardness is irrelevant here too.

While I appreciated the historical background that George included in his
earlier discussion, I'm not sure that this part of his discussion is
either correct information or an improvement in our understanding.

My view on these definitions:  simplify, simplify, simplify

"carbonate hardness", when used in the hobby refers to alkalinity.
Otherwise it appears to be a meaningless term and should be avoided.
If there is an accepted definition that equates carbonate hardness with
temporary hardness then this only emphasizes our need to avoid using the

"hardness" used in any other context always refers to calcium and
magnesium; either their total concentration or some part of their
concentration.  The various subdivisions of hardness (temporary,
permanent, noncarbonate) are of little or no value in aquarium keeping.
Only the whole term (hardness, general hardness, total hardness or
calcium-magnesium hardness) is useful, and they all measure the same

Roger Miller