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Re: [APD] GH vs. PPM

Thanks, Roger.

I think I understand --  anyway, I'll have time to give it
more thought after I clean up the clock puddle. 

thanks, again,
--- roger at spinn_net wrote:

> Scott wrote:
> > For those of us that didn't take organic chemistry
> because
> > we thought it was about clocks that dripped over the
> edge
> > of tables, how do the organic acids come into play?
> In exactly the same way that inorganic acids may come
> into play.  Any 
> acid that
> is disassociated at the ambient pH and becomes more
> associated at a pH of 4.5
> or so adds to the buffer capacity of the water.  It will
> be measured as 
> part of
> the KH.
> Unlike the relatively small number of simple inorganic
> acids there are
> approximated a gazillionkabillion different organic acids
> -- well, more than
> two -- that can have an effect.
> Some of the organic acids are large and can be massively 
> polyprotonated. "Polyprotonated" means that each molecule
> can associate 
> with more than one
> hydrogen ion.  Phosphate is the most polyprotonated
> inorganic acid that we
> usually deal with -- it can associate with up to three
> hydrogen ions.  Some
> especially large organic acids may be able to associate
> with thousands of
> hydrogen ions.  All that associating give some of those
> organic acids rather
> poorly defined acid-base characteristics.
> To make the situation even more difficult, some of those
> acids are not very
> soluble and will remain in a solid state while still
> behaving like 
> acids.  Part
> of the organic fraction in soils and peat behaves that
> way.  The insoluble
> organic acids will not be measured as part of the buffer
> capacity of the water
> but can still have darkly mysterious effects on the water
> chemistry. They can
> destroy the bicarbonate content of the water; they create
> an odd pH dependence
> in the cation exchange capacity of soils.
> Other organic acids are small and about as simple as
> inorganic acids.  Their
> simplicity is offset by the fact that we can't readily
> identify the acids in
> question and by the fact that there are a number of
> possible 
> candidates, all of
> which may be present at any one time.
> The other complicating factor about organic acids is that
> -- unlike inorganic
> acids which usually won't be there unless the you add
> them yourself -- 
> they can
> be generated by activity in the aquarium.  Some may be
> generated directly by
> plants or fish and released into the water.  Some might
> be secondary products
> from fungal or bacterial breakdown of organic material in
> the tank or 
> filter. Probably the most difficult to understand are
> those that might 
> be generated by
> fungal activity in the substrate or in decorative wood in
> the tank  Wood (or
> more precisely, the organisms breaking the wood down) may
> produce acids from
> the time it goes into your aquarium, or it may be
> perfectly benign for months
> or years, then start producing acids only after a
> population of acid-producing
> fungi -- probably growing in an inobvious, non-fruiting
> stage deep inside the
> wood -- grows to a signficant size.
> The organic chemistry of aquariums is something that we
> know relatively little
> about.  While it may be responsible for a lot of
> different effects in an
> aquarium I doubt that the organics have much at all to do
> with melting watchs
> or with hard-to-remember experiences during our youths.
> Roger Miller
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