Re: General Hardness GH vs. Carbonate hardness KH

[Thomas Soelter <Thomas.Soelter@ruhr-uni-bochum.de>]

Hi William,

KH (carbonate hardness) sizes the concentration of hydrogen carbonate (HCO3- an
anion). General hardness or total hardness sizes the concentration of calcium and
magnesia ions (Ca++ and Mg++, cations). At higher pH values hydrogen carbonate
turns to carbonate (CO3--). Those Ca/Mg++ ions and carbonate may fall out  and
make those ugly white crustation (I think the english word is lime, CaCO3) near
to the water surface.

You are using ion exchange resin that exchanges ++ ions with 2 + ions (sodium or
potassium) but only these (the reason why KH stays at the same level as before).
That is the reason why the regeneration of the resin requires potassium salt.

That way hardness is reduced but electric conductivity and salt concentration
rises. Maybe our dwarfs cichlids like salt more than hardness. I don't know.

Alternatives:
*you could use another resin that changes ++ ion with acid H+ (regeneration with
hydrochloric acid: a little bit dangerous). Due to the low pH of the water after
ion exchange HCO3- turns to CO2  +  H2O. Aerating for a few hours (or days) will
reduce the carbon dioxide and mixing with some tap water will raise the pH to an
acceptable value. The result is soft water with low salt concentration. PH
measurement is absolutely necessary before putting to the tank !!.
*RO-devices

HTH,
Thomas


William M. Groth wrote:

> I am sure this has been covered many times but here goes.
>
> I have a water softening unit which uses DI resins which are regenerated
> with Potassium salts.  We also have a carbon unit for the residential system
> which removes chlorine, chloramines, etc.
>
> We have tested our water and the GH was approx.  .5 dH (less than 10 ppm)
> but the KH was approx. 9.5 dH ( or 170 ppm).  Does anyone out there know just
> exactly what the Tetra test kits for GH/KH actually measure and why the
> carbonate hardness KH would be so much greater than the general hardness GH??
> ______________________________________________________________________
>
>        William M. Groth
>        groth@ruf.rice.edu
>        Senior Staff Auditor
>        Internal Audit Department
>        phone: (713) 527-8101 ext.3759
>         fax:  (713) 285-5927
> _____________________________________________________________________
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