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Re: Substrate Heating/Circulation
> > Joanne wrote:
> > I am also wondering if just substrate circulation by UGF is as good as
> > heating cables since my 125 gal tank looks just as good as a friends 110
> > gal tank with Dupla setup [snip]
>
In response Charles Bay wrote:
> However, could this slow convection not also be achieved through greater
> attention to slow UGF filtration? Maybe bubble-lift tubes have a
> purpose after all?
>
In theory, I agree with the above. Prior to the popularity of powerheads,
UGF were used extensively with planted aquaria. Although I was not one of
those users, I know others were (including Thomas Horeman of
Rataj/Horeman fame; Tom even marketed a tube style UG filter in the UK
until molded plastic varieties gained the competitive edge.) IMHO, the
slow flow UGF may not have the lack of long term stability (or whatever)
that George Booth mentions when he describes the relative success of his
different systems. I recently
set up a few tanks with bubble-up UGFs, but do not see any clear
advantage over systems without any artificial flow. Some of these tanks even
have soil under coarse sand, and the flow is not strong enough to blow out of
the substrate.
To date, I have not tried any UG heating cables, but I am still curious about
their potential advantages.
>
> My current worry is that undergravel heating cables may overheat the
tank > > too much. [snip]
>
> If your tank is already 90F, the coils must heat
> the area to 90+F to generate a convection.
>
This is precisely the reason that I have not set one of these up. People
who live in warm climates may not want to run the AC or chillers to
maintain desireable tank water temperatures.
>
> tied to the substrate's bacterial activity, you can't turn the heat
> off when the tank gets too hot, lest you risk anaerobic activity in the
> substrate.
Some people (on the net) with heating cable systems have already reported
changes in plant growth which could be attributable to temporary
elimination of the cable heating.
>
> I had thought that it would also be a good way to do CO2 injection
> right into the substrate, but I now think that if I keep the flow-rate
> low (like I think it should be), I won't be able to get enough PPM CO2
> injected into the substrate.
Of course, when one uses peat or other organic matter in the substrate, CO2
is a bi-product of its decomposition- one of the advantages of using such
substrate additives.
George Booth wrote:>
> Any hydrologists out there? TOA claims that they found very little
> in the way of anaerobic areas when they were researching substrates
> in streams and lakes with plant growth. Who knows? The ground water
> doesn't need much oxygen - the substrate needs to be somewhat
> anaerobic ("anoxic", I think) to allow reducing reactions to occur.
The studies that Horst and Kipper describe were done in South East Asian
streams. Clearly, the conditions that they describe may be necessary for
certain plants, including Cryptocoryne. I am starting to realize that at
least some crypts do not do well with roots in anossic state. This is not
true for otheractively growing plants. We all know that many other
plants, in nature grow in stinky anaerobic muck.
It may be that the degree of
anaerobicity (perhaps measured in terms of redox potential) needed in the
substrate varies with the type of nutrients available, and needed by the
plants. If the water is deficient in iron, then iron in the substrate
must be in reduced form so it can be utilized by the plants. If the
plants can get nutrients from the water, or may even be able to use
oxidized nutrient, then the substrate can be or may need to be with
oxygen. Similar arguments may apply to other nutrients, including
Nitrogen.
Keeping the substrate with sufficient O2 can be achieved in many ways
without the use of heating cables. Some of the ways that come to mind are:
use UGF, slow flow or other; use coarser gravel or thinner layers( e.g.
1-2 inches); using materials like vermiculite to keep substrate loose; do
periodic gravel washes; utilize burrowing or digging
creatures; have plants with robust root systems, like Echinodorus (sword
plants), and finally, heating the tank from below (which I still believe
may have some value, including increased bacterial metabolism) Each of
these approaches may need a different strategy for adding nutrients and
selecting suitable plants, etc.