Substrate Heating

I have finally decided to fulfil a long held dream - a large plant tank.
I have acquired a 120 gallon glass tank, 72"X18"X24". I have also read,
studied, maybe even memorized the book "The Optimum Aquairum", as well
as everything George Booth has ever published on the subject of planted

In both "The Optimum Aquarium" and in George Booth's series of articles
on his plant tanks, a great deal of emphasis is placed on substrate
heating to promote nutrient uptake by plants in the tank. Dupla makes
one type, Sandpoint USED to make another, both are (or were) expensive.
Various people on the net have suggested alternatives, either wires
imbeded in the gravel hooked up to a home-made transformer or slow flow
U/G filters, etc. I can't afford to go the Duplamat/Duplaflex route (I'm
a Civil Servant) and I lack the knowledge to play with home-made
transformers, so I have cast about for yet another alternative.

I found several references on the net to the possibility of using a
manifold of pipes embeded in the gravel, through which heated water is
circulated. The heat would be provided by an aquarium heater in a small
insulated tank, separate from the main tank. The water in this tank
would be maintained several degrees higher than the main tank's water
and circulation would be provided by a small water pump. Various
materials were mentioned for the piping, from plastic airline tubing to
PVC to titanium tubing. One kind person even went so far as to provide a
table giving heating coefficients for various materials.

At the time, I thought that this manifold method "should" work, but was
involved in other things and couldn't try it out for myself. I saw
several posts which claimed that not enough heat could be transferred
using the most likely material, PVC piping. But I never heard of anyone
who considered copper. It is readily available in 1/2" diameter lengths
and is easily worked. Very few materials have copper's ability to
transfer heat. It's one drawback, and I admit that it is a major one is
its potential toxicity to the inhabitants of the tank. But what if the
copper was coated with epoxy? I doubt that the thin layer of epoxy
necessary to isolate the bare metal from the aquarium water would hinder
copper's ability to transfer heat by conduction.

Another concern that was expressed was the small temperature
differential which would likely be produced by a network of warm pipes,
as opposed to the supposedly large differential produced by Dupla type
wires. Well, in reading various sources it seems that there is at most a
5 degree differential between the temperature at the bottom of the
gravel and the tank's water in a Dupla type set-up. I'm sure that this
could be achieved or even exceeded by a network of copper tubing.  

My tank is located next to a large closet which provides the perfect
place to put the small holding tank necessary to hold the heated water,
with the copper tubing being let through the wall between the closet and
the large aquarium. My Eheim is already in the closet and I find the
arrangement perfect - the equipment is easily accessible but completely
out of sight.

I would appreciate any feedback on this idea that anyone might care to
give. Does anyone use a manifold of heated piping in their gravel to
provide "warm feet" for their aquarium plants? Can anyone think of a
reason (or reasons) why it wouldn't work? 


James Purchase
Toronto, Ontario
jpp at inforamp_net