Re: Diffusion

> From: gomberg at wcf_com (Dave Gomberg)
> I was just reading a limnology book at the lib yesterday and for a gas in
> solution (the example used O2) to diffuse 10m in a lake that was otherwise
> undisturbed takes about 600 YEARS.  So forget this mm per day stuff.  Their
> point was that diffusion is VERY SLOW.  

I think your quote is out of context Dave. If you are referring to
diffusion in water (which is never undisturbed) these numbers can't
be applicable. If you are referring to oxygen diffusion through 10m
of very compact clay at the bottom of a lake, I cannot judge if this
is reasonable.

Look at it another way. Aquatic plants grow in natural conditions without
benefit of heating coils and undergravel filters and in compact
substrates. Undoubtedly we can improve these conditions by providing
more permeable substrates, by heating the substrate and by inducing
low rates of circulation in the substrate.

> From: Nick Livingston <nickliv at halcyon_com>
> Subject: Re: Vermiculite diffusions whatsit-business
> > uprooting via underwater erosion. As to fresh vermiculite being
> > loaded with "un-bonded" sites; this should not be a problem after
> > the first few days after water has a chance to penetrate the new
> > substrate. The largest ion concentration is NH4+ and then probably
> > K+ and Ca+ and Na+. The percentage of each ion type at CE sites is 
> > in dynamic equilibrium with the concentrations of those ions in the 
> > aqueous solution. CE substrates simply provide a higher local 
> > concentration of those nutrients.
> If it's not too much trouble, could someone translate this into English 

Which part? Vermiculite (or other materials) will not have "un-bonded"
cation exchange sites since after a few days, these sites will be occupied
by ions present in aquarium water. The proportions of each ion will
depend upon the concentration of those ions in the water. This is a
dynamic equilibrium. When the concentration of a particular ion in
solution increases, the relative percentage of that ion loosely bonded
at a cation exchange site will increase. In other words, these bonds
are not static. The concentration of "nutient" cations in the substrate 
will be greater than the concentration in the general aquarium water.

> From: krandall at world_std.com (Karen A Randall)
> > So far I have good results with vermiculite, humus & gravel for about
> > two months.
> Have other people had success with vermiculite long term?  I'm glad your 
> tank is doing well, and hope it continues to, but a two months, it's hardly 
> even settled in yet!

True enough. How long does it take for the effects of anaerobic decay to
show up? In a correspondence with Shaji some time ago, he said:

"I used it in a 55 gallon tank.  The bottom third
of the substrate was equal parts by volume of potting soil, peat and
gravel.  The rest was washed gravel.

The substrate did go anaerobic ( I could see the bottom of the tank
darken) for two or three months, but after that, everything was fine."

I infer that this going anaerobic happened relatively quickly. Anybody
know how long it takes? Shaji? Anybody else have any experiences with
vermiculite they'd care to share? Thanks to all for the info so far.

BTW, I am using a higher proportion of soil as part of an experiment
with Aponogeton madagascariensis. I am hoping to stimulate the plant
to store reserves of energy into the tuber instead of depleting it
as frequently occurs in plain sand substrates. There may be other factors
aside from the substrate which are important for long term growth of
the lace plant. My feeling is that temperature is such a factor.