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 

 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.