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Re: APD V3 #245 - carbinate hardness

Jim Wilson wrote:
> In a previous post I asked: Is there a benefit to adding CaCO2 	> to raise my KH instead of NaHCO3? I know that CaCO2 also raises > GH.
> OK OK I'm the best typist in the world and do know that it is 	> CaCO3 and not CaCO2.
> But did I stump the panel?  Or has this question been answered 	> too many times already?

Hi, Jim,

First of all, sodium bicarbonate, NaHCO3, will raise the pH of your
water and will have *NO* influence on hardness (if one discounts any
change in hardness due to the change in pH).

Calcium carbonate, CaCO3, if dissolved, *will* raise the hardness, both
carbonate hardness (commonly referred to as "KH" [from the German
KarbonatHaerte] or temporary hardness [because it can be removed by
boiling the water]) and total hardness (commonly referred to as "GH"
[from the German GesamtHaerte] or "TH" = Total Hardness).

Total hardness of water is comprised of temporary hardness and permanent
hardness - that part of hardness that can *not* be removed by boiling
the water. That is why you *will* raise Total Hardness (GH = TH) if you
raise Carbonate Hardness - by *any* means.

I qualified the effect of CaCO3 on hardness by saying that it has to be
dissolved, otherwise it will be just "gravel" on the bottom of your tank
or filter (limestone, coral, etc.). 

The reason is that CaCO3 is not very soluble in water. But the presence
of *excess* CO2 solubilizes it, converting to the bicarbonate
(Ca(HCO3)2) which is more soluble. [Ca(HCO3)2 is only a "nominal"
formula, because in solution Ca(HCO3)2 is loosely associated with more
CO2 & H2O molecules that shown in that formula & "solid" Ca(HCO3)2
normally can not be isolated - it decomposes.] 

Thus if one removes excess CO2, say, by photosynthesizing plants, CaCO3
will precipitate - it does not have that excess CO2 needed to solubilize
it. At the same time the pH of the water will go up significantly. This
happens quite often in tanks with vigorous plant growth and *not*
fertilized by CO2 (see biogenic decalcification, APD V3,#277).

If you want to *increase* the hardness of your water, the simplest
method that comes to mind is the addition of marble chips (obtainable in
garden supply stores) to your filter. It will raise hardness slowly,
without harming your fish. (But why do you want to increase hardness?)

Hope that this helps somewhat. If you need more, just ask.