[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: GH and KH from calcium hydroxide

On Wed, 30 Jun 1999, Larry Jones wrote:

> I don't think CaOH will work for increasing your KH.


Calcium hydroxide (Ca(OH)2) is a strong base and it will raise KH as well
as GH.  The OH- reacts with CO2 to form HCO3- or with HCO3- to form CO2--
+ H20.  With either reaction (and at constant pH) one equivalent of added
OH- raises the KH by one equivalent.  Add 10 mg/l of Ca(OH)2 and you will
increase both the alkalinity and general hardness by 13.5 mg/l as CaCO3,
or about 0.75 degrees KH or GH.

> Also KH is the measurement of Carbonate Ions, while GH is a measure
> of Sulfate ions, mostly Calcium sulfate and Magnesium sulfate.


KH measures alkalinity which is usually determined by the bicarbonate ion
in solution.  The carbonate ion is exceedingly rare in normal freshwater
aquaria at near-neutral pH.  GH has nothing to do with sulfate.  It
measures dissolved magnesium and calcium concentrations regardless of what
the countering anion may be.  Formally, general or total hardness (GH)
also includes the concentration of strontium and barium but those are
relatively rare beasts.

As others have said, don't add calcium hydroxide directly to your

Roger Miller