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Re: 150 watt substrate heater cables

Scott H. wrote, in response to George Booth's description of the difference
between the Dupla and Dennerle methods of substrate heating:
"Since the Dennerle and
Dupla models are essentially opposites regarding the convection issue,
it would be nice to see some hard data to help, er, clear the market.
They can't both be right!  Or anyway, they can't both create optimum

That is correct only if the sole or even the major benefit to be obtained
from substrate heating is the formation of convection currents. We don't
_know_ that, at this point in time it is still only conjecture. Both methods
_may_ work equally well, in an aquarium situation, so _both_ companies may
be "right", whatever that means....

"I would think that measuring temperature differentials a few inches
apart in substrate, underwater, would require terrific precision and
perhaps an elaborate arrangement of tanks with different test and
control conditions.  Detecting and measuring convection, would seem to
be even harder to study."

I'm _not_ an engineer, by any stretch of the imagination. But it _is_
relatively easy to measure at least gross differences in substrate
temperature within the space of an inch or so, using relatively easily
obtained instruments. Before I bought electric cables for my large tank, I
used a homemade manifold of epoxied copper tubing under the gravel of the
tank. I got the idea from an article in AFM done several years ago - in the
article, the authors used a PVC manifold. I pumped heated water through this
manifold - the water was heated in an insulated exterior container (an extra
10 gallon aquarium with an Ebo Jager heater) and pushed through the manifold
using a big Eheim pump. Clumsy I know, but it was worth a shot.....

Anyway, when the thing was operating I _was_ able to measure a heat
differential within the substrate using a very precise mercury thermometer.
Many years ago I used to play around with photography and did my own
darkroom work. I have a mercury thermometer made by a company from England
called Paterson and it will measure to one quarter of a degree (F) or to 0.2
degrees C. It was made and sold to measure the temperature of color
processing chemicals used in film processing. How accurate it is, I don't
know, but it has more precision than any thermometer sold for regular
aquarium use. (I know the dangers I was risking by sticking a thin glass
bulb containing mercury into the gravel - I don't recommed it to anyone.)

Using the termometer, I was able to see visible differences in substrate
temperature throughout the substrate bed merely by inserting the thermometer
into the gravel. I knew where the heating manifold was and the highest
temperatures were recorded directly over the tubes. The area of substrate
between the tubes was several degrees cooler - I don't remember exactly how
much cooler, I think that it was only around 3 degrees - that info may be
somewhere in the archives, because I think I described it before. I seem to
recall that it was not as much of a difference as George (and others) were
recommending to be "enough" to cause the circulation patterns that a system
like the Dupla cables is capable of.

I was never able to attribute anything good or bad to the presence of the
undergravel heat. The setup had major problems and was eventually dismantled
but I believe that the problems were related to the way I had set up the
substrate (i.e. a little bit of this, a little bit of that and a whole lot
of several other things......I had attempted to listen to too many "experts"
instead of sticking to something tried and true and simple).

James Purchase