Re: Peat Moss vs. Oak Leaves

["David A. Youngker" <nestor10@mindspring.com>]

From: Randy Carey
Sent: Friday, November 23, 2001 1:09 PM

> The chemical value of peat (value for us aquarists)
> is that it removes the Ca and Mg ions by replacing
> them with Hydrogen ions.  So it does both:  removes
> hardness (by removing the metal ions) and increases
> acidity (by increasing the hydrogen ion count).

Aye, we have reduced "hardness" by x %, but exactly how have we affected the
other components? After the divalent earth alkalis and iron are replaced,
and bicarbonates consumed, there's still the overall effect on "permanent"
hardness, conductivity and TDS.

Until I have the chance to study these, I still reserve a direct comparison
to RO/DI as a little weak. And the collection of electronic testers I'm
assembling will make the task both more accurate and precise.

> I see in them the correlation between the drop of pH
> and the drop of calcium:  a fast drop in one correlates
> to a fast drop in the other, and a leveling out in one
> correlates to a leveling out of the other.

Let's see - that's two hydronium per calcium, minus one for the bicarbonate
consumed...

> But I think that this comment was made because
> --despite an ample supply of peat-- the peat lost its
> effectiveness.  Because hardness was not reduced to
> zero, the assumption was that hardness is not removed
> as effectively...

Not a blind assumption, though. You see, another consideration in the pH/GH
arena: Why is the same pH endpoint demonstrated with the use of distilled as
base?

> At some point, the effects of peat were arrested --
> as if some equilibrium was reached...

This is going to be the tricky part, and the main reason I'd planned to
continue forward with "artificial" samples of freshwater. There is obviously
some cationic exchange capacity as well as a weak dissociation of some of
the humics or other acids involved. Which is the more dominant, and does the
percentage contributed by each, though not specifically quantifiable across
collection samples, at least fall into some type of discernible pattern? And
what does its _anionic_ exchange capacity look like?

An easy initial assumption would be that the cationic exchange capacity
would be the predominant, as it doesn't take too much hydronium from
dissociation to affect distilled samples. The harder part would be, as you
ask: Why does the pH of _both_ reach the same "equilibrium"?

(Speaking to myself)Is that even a valid question, considering I've only
worked with two brands of peat?...

-Y-

PS to list:

Concerning the difference in Maple and Oak leaf decomposition, has anyone
read the Cryptocoryne article in the recent Planted Aquaria Magazine?

Hmm...seems *Beech* - derived soil is fairly acidic, weighing in at around
4.5 or so, and doesn't break down too rapidly. Does the study previously
mentioned (damn, but I wished I'd paid attention to that part of the thread)
say anything about the suitability of Beech leaves to our purposes?



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