🚀 go-pugleaf

fernando@aplcomm.jhuapl.edu (Fernando Pineda) writes:

>Keith's post on the matter was a suggestion that there were at least
>two kinds of hardness. An interesting suggestion, but what's the
>quantitative implication? Is there a conversion factor or not?

I'm not suggesting, I'm reporting.  There are many kinds of "hardness"
which are measured.  The term is applied to any practically any
disolved substance in water.  Here's a micro coredump of what is
important for aquarists as I understand it.  It may not be entirely
correct; others are welcome to throw in their input.

Total Hardness: total amount of di- and trivalent metals in the
sample.  In tap water it's made up almost entirely of calcium and
magnesium.  Salt water has large amounts of all kinds of metals and is
very very hard so saltwater keepers don't pay attention to this
hardness.

Alkalinity: a measure of the total acid binding ability of the sample.
Carbonates, bicarbonates, borates, hydroxide and other such ions
participate in this test.

Carbonate hardness: a measure of only the carbonate buffering ability
(the famous H2CO3 <=> HCO3- <=> Co3-- equilibrium reactions).
Alkalinity and carbonate hardness are often about equal as carbonates
often dominate water buffering.

Calcium hardness: a measure of only calcium ions.

All of the above can be expressed in "CaCO3" equivalents.  This *does
not* mean that CaCO3 was measured, it's just one common way the
results are expressed.  If your kit expresses carbonate hardness in
CaCO3 that does not mean the carbonates came from CaCO3.  It means
there are as many carbonate and bicarbonate ions *as if* X amount of
CaCO3 had been added to pure water.  It tells you nothing of what
substances contributed to this hardness.

Ppm and mg/l are other common units used.  In addition, all excepting
perhaps calcium hardness for which I'm not sure can be expressed in
"degrees" of some form.  The problem there is everybody uses different
degrees.  When "degrees" are used in the aquarium hobby, german
degrees are usually meant, though I have one book which uses french
degrees to my neverending annoyance.  But that's nothing compared to
the annoyance of getting a municipal water sample expressing things in
grains/gallon (mind you know if they were US or Imperial gallons),
meq/l and other such units.  For conversion between the various units
see Moe, p. 36.

I've been posting my replys rather than e-mailing since I'm sure there
are others who are fuzzy on this as well.  I just hope I'm giving you
a true story.  If others detect flaws I'd like to know them as I'd
like to understand this as well.

Oh, and don't you dare wimp out behind the "I'm just a poor physics
student, not a chemist" line!  It so happens I'm a physicist and I
know all of us have to have at least one year of inorganic chemistry.
So there... ;^)

For that matter, the Net is loaded with all kinds of software types
who have only had one semester of inorganic chem, if that.  If *they*
can get a grip on this hardness stuff *anybody* can.  [double] ;^)

Now, now, put down those roaster toasters.  I was only joking and it
wasn't really raunchy enough for alt.tasteless.
-- 
Keith Rogers
krogers@javelin.sim.es.com