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measuring calcium and magnesium

>Date: Thu, 09 Jul 1998 02:55:04 -0700
>From: Steve Pushak <teban at powersonic_bc.ca>
>Subject: measuring calcium and magnesium
>I propose that we stop using units of hardness to refer to concentration
>of magnesium and calcium. The appropriate units for those things are in
>ppm or mg/L of Ca++ or Mg++.

Okay, once the Tetra hardness test kits that I purchase once every few
years start reading in units of ppm Ca++ or Mg++, I'll start using those
measurements.  Until then, I'll include a conversion factor for GH and KH
as dH * 18 => (CaCO3) equivalent.

It's very interesting to read the discussion on ppm Ca++ determined by CaO
or Ca++ or CaCO3, or ppm Mg++ determined by Mg++ or MgCO3 or CaO or Ca++ or
CaCO3, but unless I'm going to break out my LaMotte water test laboratory
(a gift to me from a friend, but worth $1500) for all of my water tests, I
think I'll just give the measurements that my little bottles of Tetra
reagent produce (tap water = 5 dH KH, 9 dH GH).

I understand that this doesn't provide me with Ca++ or Mg++ amounts, but
the North Texas Water District is kind enough to supply these numbers with
a simple phone call.  I still haven't read anyone's suggestion as to what
units of measurement we should be required on this list to use when
providing alkalinity.  After all, we really shouldn't always assume that
alkalinity is primarily due to carbonates when we have so many tanks with
high humic acid content in the water.

Maybe we should all be required to use Kelvins or degrees Celsius for
temperature instead of Fahrenheit too.  After all, if we measure per
half-degree Celsius, we can get roughly the same granularity as with

If someone on this list is prepared to identify the definitive "correct"
way to keep aquatic plants, making every other method "incorrect" then I
accept that perhaps their units of measurement are correct as well.  In the
meantime, I can handle dH in units of CaCO3 equivalence, ppm of CaCO3
equivalence, or ppm Mg++ or Ca++.  It might be better to just post
conversion tables in the APD FAQ than to argue over which test kit provides
units that are most appropriate for the aquaria hobby.


David W. Webb
Live-Foods list administrator