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Re: under gravel heating cables

 Jeff Coart wrote: I can't tell you if the cables improve plant growth or
not since my tank
> has always had them. I can tell you that people like Tom Barr would
> suggest you put the money into your CO2 setup instead which is probably
> good advice.
Unfortunately,  unless you build them yourself, the low voltage "Dupla"
> type are very expensive.

I disagree, the Dupla Thermik substrate low voltage heating system can be
bought for under a hundred dollars. While I agree with you that CO2 should
be a main priority if finances are limited, I also believe that substrate
heating is conducive to long term stability in an aquarium.

 >Lots of healthy plants with strong roots probably do more
> for your substrate than heating cables and based on what I've read on
> the APD there are a lot of people out there who don't have them and
> still grow beautiful, healthy plants.

I don't think the issue is whether or not you can grow healthy plants
without them. The added benefits to me is the issue. Which are:
I quote Pablo Tepoot, the heat from the cable creates a very slow vertical
current of water. This current is generated due to the fact that heated
water rises and colder water sinks. Gentle circulation of the tanks water
helps to prvent the buildup of nitrogenous waste, the gentle circulation
causes the water to flow through the upper area of the substrate which is
composed of more permeable gravel. This upper layer is the aerobic zone -
oxygen rich. This area contains aerobic bacteria. The ammonia in the water
that flows through the upper permeable substrate is oxidized into nitrite
(NO2) by the bacteria. This nitrite is then converted by other bacteria into
nitrate. Some of the NO3 filters down into the "anerobic zone" (oxygen poor)
The anerobic dentrifying bacteria in this area convert the NO3 into nitrogen
gas. The bacteria do this by using the oxygen in the NO3.The resulting
nitrogen gas is then dissipated. (I say, the point being that your substrate
is turned into a huge biological bed as well as assists in cycling at the
setup phase, which is why I probably never had detectable levels of
Ammonium, Nitrite, Nitrate during the cycling phase.)
I quote Dupla, We know from detailed observations in nature, that water is
constantly flowing through the plants root areas. This is due to ground
water currents. This movement of water may be horizontal, but can also occur
in a vertical movement due to changes in ground water level. This phenomenon
has a great advantage: the water flow constantly supplies oxygen to the soil
and thus prevents any decaying and blackening of the substrate. Nutrients
are also continously supplied to the plants roots. With a substrate heating
system we achieve a water circulation which comes close to that in nature,
therby obtaining a healthy and breathing substrate. Warm water rises to the
top, cold oxygenated water drops below.
I run my cables 24/7 in a very warm (year round) office in one aquarium, and
never have a problem with too much heat. There isn't too much to them to go
wrong. I can tell you that in a 55 without them I had a 76 degree water
temp, and the substrate had to be 10 degrees below that and was black in
spots. Plants were doing okay at best, at least it appeared that way. I tore
it apart and installed heating cables and all other factors being identical
(water chem, ferts, water temp, etc.) I have seen a tremendous difference in
growth. I don't know if the substrate heater is the sole cause, but an
educated guess would say it contributed to the difference. I write this not
to convince anyone that it is the only way for them or to produce good plant
growth, but to allow people to make up their own mind based on the implied
benefits.  Don Matakis