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Re: [APD] Under Gravel Heating -- or - Serious differences (re temps)

One method of substrate heating is to use coils to create
temerprature differntials in the substrate, which then
promote the flow of water downward from the water column
into the substrate where it is cooler while the hotter
areas above the heater wires convect water upward out of
the substrate and into the water column. If the substrate
is heated evenly, this effect won't happen. The value of
this convection is that it's thought by some to keep the
substrate "fresh" by bringing in nutrients from the water
column and and preventing the build up of too much bad stuf
by moving it up and out of the water column. (Of course
plant roots can do the same thing.)

George favors the differential temps method of substrate
heating a la Dupla.

With very low wattage coils that stay on all the time this
temperature differential effect probably doesn't as well or

With undertank heating, this effect probably doesn't happen
well or at all.

This doesn't mean that "evenly" heating the substrate
doesn't have its good point -- it's a relatively efficient
way to heat an aquarium compared to tube heaters in the
water column. And it keeps the roots from being cooler (of
course some unsulation under the tank will passively keep
the roots from being cooler).

The benefits of the differential heating have been noticed
by some aquatic gardeners that have tried it and not by
others. Although many of the the more notable aquatic
gardeners have tried it (e.g., George and Karla Booth,
Karen Randall, Tom Bar, etc.) it never really seem to be a
widespread practice and it appears to be practiced by even
fewer to day.

The equipment costs for substrate heating tend to be much
higher than for water column heating.

As for discussion on the list, this topic always brings a
flurry of posts -- the archives are basted with the butter
richness of this hot topic. Also, some good info on
TheKrib.com, last time I look. In particular mail posts
about making your own cables and so on.

Good luck, good fun,
Scott H. 
--- David Terrell <dave at terrellclan_com> wrote:
> I haven't considered anything just yet...it was just a
> thought as I read
> through George's site.  I don't see why this wouldn't
> have the same effect
> of coils, really.  Adding heat in or under the substrate
> would add heat in
> or under the substrate!  Right?  Aparently not.  It was
> just an idea I
> thought would be interesting to discuss in the list.

S. Hieber

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