# Re: Hardness in ppm

```> From: George Slusarczuk <yurko at warwick_net>
> Subject: Re: Water hardness in ppm
>
> Hi Paul,
>
> Plant Digest, V3 #370), I agree with the results of your calculations,
> but not necessarily with your line of arguments and/or conclusions.

I may have left the impression that I _like_ the GH and KH units.
I don't!

> > GH and KH are odd units to use in lots of ways, but at least one is
> > in no doubt what they are.
>
> Well, not exactly. Because there exist different scales of "degrees" of
> water hardness, offhand one DOES NOT know *which* "degrees" are being
> used -- and that creates substantial uncertainty!

I know that the many "degrees" can cause problems, but I think
that "GH":- Gesamt (total) hardness is pretty definitely the German one.
Likewise, KH.

> Atomic weights DO NOT enter into this particular calculation, if BOTH Ca
> and Mg are expressed as *mg/L CaCO3*. A simple subtraction of "calcium
> hardness" from "total hardness" will give one "magnesium hardness"
> expressed as CaCO3, i.e. that part of total hardness caused by
> magnesium! Pure and simple.

Agreed.  I suspect that the idea of expressing Mg++ as a CaCO3
concentration is causing some confusion, though.  I tried to explain the
relationship in my posting.

> Admittedly, this CAN be considered to be in "molar units" in the sense
> that 100 ppm of *calcium water hardness* equals 0.001 mole/L (=
> millimole = mmole) of CaCO3 and 100 ppm *magnesium hardness*, *EXPRESSED
> AS CaCO3* is also 0.001 mole, but of MgCO3, i.e. they are equimolar.
> (Which is also your conclusion!)

This is the bit I like about hardness in ppm CaCO3!  divide the
number by 100, and you get the millimolarity of the Ca++/Mg++ in the
>
> In my opinion, using perts-per-million of "calcium carbonate hardness"
> is just as easy, or easier than starting with "degrees".

Agreed, provided it _is_ calcium carbonate hardness, and
explicitly stated to be that.

The next time I report on one of my tanks, I'll give everything
as millimolarities!        ;)

--