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RE: Carbonate Hardness / Alkalinity



Hi Everyone,

I'm not interested in starting a war here, but I hate to see assumptions
passed off as fact. Water chemistry confuses a lot of us (I count myself in
that number) and a lot of space has been taken up with discussions of just
exactly what the different parameters are and how they are measured. In APD
V3 #325, Dave stated the following in response to a descriptive post by
George Slusarczuk:

> I have beaten my head against the wall over this many times on this list.
> Your post is excellent but one point should be mentioned. On the APD we
> have agreed for the purposes of simplicity that carbonate hardness IS
> alkalinity (by our definition).

I take exception with the "by our definition" part of this comment. In most
aquatic environments, and in most of our tanks this might be true, but that
doesn't mean that they are equivalent in ALL situations or all tanks. The
following exerpt is from the Reefkeeper's FAQ:

    Alkalinity is often confused with carbonate hardness since both
    participate in acid neutralization and test kits may express both
    in either of the three units.  However, carbonate hardness is
    technically a measure of only the carbonate species in equilibria
    whereas alkalinity measures the total acid binding ions present
    which may include sulfates, hydroxides, borates and others in
    addition to carbonates.  In natural seawater, though, carbonates
    make up 96% of the alkalinity so equating alkalinity with
    carbonate hardness isn't too far off.

Just because most of our tanks don't contain signifigant amounts of these
materials doesn't change the definition of the two terms. Carbonate Hardness
is NOT Alkalinity by definition and we should not, IMHO, be adding to the
confusion by saying that they are. The initial confusion is probably caused
by the fact that most discussions of both Hardness and Alkalinity use
equivalents of CaCO3 as their units and a lot of people think, mistakenly,
that since the term "CaCO3" is common to all of the tests, that they are all
measuring the same thing - which they are definately not doing.

Let's not add to the confusion faced by a lot of aquarists by redefining
terms to suit our own ends.

Just my two cents.

James Purchase
Toronto, Ontario