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Re: what's in a name?

> Date: Tue, 22 Jul 1997 16:50:08 -0600
> From: George Booth <booth at hpmtlgb1_lvld.hp.com>
> Subject: Re: Aquatic Plant Growth
> > Date: Tue, 22 Jul 1997 09:04:37 -0500 (CDT)
> > From: eworobe at cc_UManitoba.CA
> >
> > (while Im at it, why dont we drop the term KH and just use the term
> > alkalinity?)

I agree with Dr. Dave on this, and I think the following illustrates why.

> Because "KH" is carbonate hardness (CO3- ions) and alkalinity is
> carbonate hardness plus other factors that contribute to acid
> buffering (like phosphates).  In the "ideal" freshwater environment,
> the only buffering would be from carbonates and we could use the terms
> interchangeably.  But most water is far from ideal in this sense, so
> we should not use them interchangeably.  IMHO, of course.

Carbonate hardness as used in technical literature is that part of the
general (Ca-Mg) hardness that is balanced by alkalinity (mostly
bicarbonate and carbonate ion).  The term is abused in aquarium

> The CO2/pH tables are based on carbonate hardness, not alkalinity. It
> would be misleading to call them "CO2/pH/alkalinity" tables because
> aquarists dealing with less than "perfect" water would not get correct
> results.

The CO2/pH/KH tables are based on bicarbonate concentrations.  The
bicarbonate concentration is converted to degrees and called KH.  The
value we measure and call KH (or carbonate hardness) is in fact

> My favorite hardness test kit is the Tetra kit.  As long as they
> persist in calling what they measure "KH" and "GH", so shall I.  I
> think it reduces confusion.

I think it promotes confusion.  I use the Tetra kit, as well and I can
show that it measures alkalinity.

> How do you feel about GH (general hardness or Ca++ and Mg++ ions)?

The question wasn't addressed to me, but I think that "hardness" alone
should be sufficient.

> George

Following is a general chemical analysis of tap water sampled a short ways
from my home. It was provided by my city water utility.  The analysis is
the average of all analyses made in regular monitoring during the 1996
calender year.  There is very little variation over time since this is
deep groundwater.  Also, I know from my work as a consultant for the city
that my home is supplied from the same reservoir that supplies the sample
site, hence the analysis should represent my tap water.

Calcium		7 mg/l
Magnesium	1 mg/l
Sodium		115 mg/l
Potassium	2 mg/l
Chloride	22 mg/l
Sulfate		103 mg/l
Bicarbonate	126 mg/l as CaCO3
Silica		40 mg/l as SiO2

Alkalinity	134 mg/l as CaCO3
Hardness	2 grains/gallon as CaCO3
pH		8.79

There are some noteable features here.

The water is soft.  2 grains per gallon is equal to 34.2 mg/l as CaCO3, or
1.9 DH.  When I calculate hardness from the Ca and Mg concentrations I get
only 1.2 DH.  I think the difference is probably due to rounding in the
city's numbers.  It's hard to measure the value with a Tetra kit, because
the color change occurs when there is too little indicator in the sample
to make the change evident.

Alkalinity is 134 mg/l, which converts to 7.5 DH.  The alkalinity is much
higher than the hardness and slightly higher than the bicarbonate
concentration.  Alkalinity is higher than bicarbonate because at this high
pH part of the alkalinity is provided by carbonate, rather than by

K and Mg are quite low - some of my plants complain about that, but it
doesn't have much to do with hardness.

The city's values don't include a breakdown into noncarbonate hardness and
carbonate hardness.  By USGS method I-1344-78, the noncarbonate hardness
is 0, so all of my tapwater hardness is carbonate hardness.  So I have
1.2 DH (or 1.9 DH, take your pick) of carbonate hardness.

My carbonate hardness at 1.2 DH is much lower than my alkalinity (KH) at
7.5 DH.  I used my Tetra kit (and a 10 ml sample) and measured my tapwater
KH at 7.5 degrees.  This is exactly the city's alkalinity value, so
apparently the Tetra kit is measuring alkalinity.

The use of "KH" and "carbonate hardness" in the aquarium hobby and
business is confusing.  We can dispense with all the confusion if we just
do what Dr. Dave suggests and use "alkalinity" when we talk about
buffering capacity.  "Carbonate hardness" correctly defined, is important
if you're running a boiler, but its pretty irrelevant to aquarium
conditions, so we should just avoid the term entirely.

Roger Miller

From Albuquerque, where hot air balloons float by my house most every
morning now.