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Heating Cables and Laterites

>In a message dated 2/9/99 6:34:54 AM Mountain Standard Time, Booth
comments on:
>>>  Now, Neil and Karen seem to be of the opinion that if substrate heat is
>>>  useful at all it is only useful in the long term (+ 1 year), while George
>>>  B. seems to feel that they are necessary for a true "Dupla style tank".
>No, George B. thinks that the benefits of substrate heat are only
>observable in the long term as greater tank stability. Karen and Neil, I
>believe, think substrate heat is only useful for increasing the rate of
>chemical and biological processes in the substrate, thus providing better

It is good that George used the phrase "I believe," because I do not think
I ever made such a statement. Although I have never used substrate heating
(aka substrate circulation), I am not willing to rule out the possibility
that it offers some value. However, I don't think it is really needed, when
the plant tank is adequately planted and well managed <g>. 

>I DID observe that the tank without coils developed
>problems (more algae, slower growth, certain plants didn't do as well)
>after 12-18 months.

When the substrate is adequately planted, and the plants are growing
properly, their transpiration processes will maintain movement thru the
substrate... at least in the vicinity of their roots.  But those of us that
do not manage our tanks on a daily or even weekly basis will invariably see
some ups and downs.. maybe a failure of some mechanical device will go
unnoticed or some routine maintanance will be missed. This is when the tank
*might* develop a problem which will affect distribution of nutrients and
the health of the substrate. I have concluded that artificial substrate
circulation might help during those situations. If substrate conditions
change after a period of time(perhaps an inevidetable situation), certain
plants might decline and be outcompeted by other species. Perhaps an even
more important reason for substrate circulation is during tank start-up (as
I _have_ previously said). Similarly, the substrate heater might be
relatively more important during the start up period (and when plants are
frequently replanted, as some people like to do on a routine basis). So, I
guess I would say that the cables (although unnecessary) could be useful in
the short-term and the long-term.

On a related point, I often use coarse sand (diam = 0.2-0.5mm). Most plants
seem to like it very well. I also use 1-3mm gravel for some plants. I
suspect that coarse sand is not advisable with heating cables because it
might affect water flow or heat transfer. 

BTW, for the past 10 years I have used Carolina lateritic soil with
excellent success.  It comes out of my back yard, so I know the source and
its track record. It is probably as good as other "laterites" that come
from North America.... maybe better, because mine is "biologically active."
<g>  Unlike some advocates of soil, I use very small quantities -- in a
similar proportion to gravel/sand as recommended for commercial laterite. I
have always wanted to do a comparison with Dupla laterite, but never got
the chance and now that the product is unavailable, I want to do this more
than ever! Fortunaly, I have a reliable and unlimited supply of my
"laterite"....maybe I will start selling it in 500g containers under the
trade name "Carolina Substrate Red." :-)

Neil Frank