Re: Substrate material and heating.

> From: "Jonathan Kalmes" <jkalmes at arcada_com>
> Date: Fri, 16 Jun 95 10:21:46 PDT
> Subject: Re: Substrate material and heating.
>      Hi all, first time on this list, but I've been lurking for a bit.  I 
>      have a few questions for ya...
>      I noticed all these posts about wierd plumbing and everything trying 
Weird? Bizarre? NOT! :-) just new and different. Water movement through the
substrate might be overemphasized. Roots also supply oxygen and
if the substrate is permeable (i.e. VERMICULITE!), some O2 will penetrate by
diffusion. Avoiding too much organic material in the substrate may solve the
problem of anaerobic decomposition there!  Too much circulation will mean
many useful reduction reactions can't take place! The stuff found in stream
beds and lakes has already undergone considerable decomposition in an 
oxygen environment before it becomes part of the substrate. It's value is
it's CEC and as a source of minerals and as a host for countless bacterial
and chemical actions. Lake mud may be an ideal substrate addition for this
reason (sterilized of bugs and others undesirable critters). Don't forget
that many people get acceptable results w/o any substrate circulation at least
for a year or two. Of course, I believe with mud or clay you want to have
some kind of substrate circulation though. Jim Kelly indicated that the 
right amount of substrate circulation is measured in drops per second if
using RUGF. Anaerobic decomposition is worse than too much circulation.
Optimum root activity certainly involves some low amount of circulation.

>      to get some water movement through the substrate and started thinking 
>      about it (because I was considering trying it).  Here's another idea 
>      for ya...  Set up a ten gallon tank underneath the main tank, drop 3 
>      or 4 heaters in it, get a small pump to pump the water through some 
>      tubing (even airline tubing would do I guess) that is coiled or 
>      "snaked" in the substrate.  Make sure the water gets returned to the 
>      ten gallon, not the tank.  Voila, instant substrate heating.  Someone 
>      please bash a hole in this idea before tomorrow, I might just try it.
Consider insulation for the little tank because the water will need to be
hot. The efficiency of wires in the substrate would be higher. If you used
aluminum tube under the gravel, thermal exchange would also be higher. Need to
paint the tubes to prevent aluminum oxidation and dissolving which would likely
be a problem with aluminum in a tank. You don't want much aluminum because it
can displace iron at the cation exchange sites. Isn't it also poisonous at
high enough concentration? I think wires is the best way to apply heat into
the gravel if you're gonna do it (cost and fuss aside). Too much of any
one mineral such as iron or aluminum can mean that other important micro
nutrients get displaced from the CEC sites and therefore can't be absorbed
as efficiently by the roots. This is an excellent argument for the use of
the prepared nutrient mixes.
>      Next...  As a substitute for laterite, will pottery clay work?  Anyone 
>      know the composition of it?  Just another thought.
Low iron concentration. Ok for CEC but vermiculite is probably better (IMHO :-)
Some clays contain carbonates and phosphates I think which are leached out
of tropical laterite. I'll let someone else comment on that. Vermiculite will also
have higher permeability and less trouble with compacted substrate difficult
for roots to penetrate. There was no comment yet on the use of charcoal which
was recommended in the TFH book. This may be a very worthy suggestion too.
It might permit other carbon reactions such as the malic acid one. I don't
know anything about malate or malic acid so I'm hoping someone can comment on 

- Steve