Organic Substrates

I'm interested to hear people's experiences with the use of organic
substrates. The following information will be useful:

1) constituents and ratios: potting soil, peat, laterite, clay, sand, gravel,
composted manure, natural soils, soil from lakes.
2) was it in pots or as a layer of your substrate.
3) did you keep fish in the tank?
4) was pH, sulfides or algae a problem?
5) what plants were suitable for this kind of substrate?
6) special filtration or circulation such as heating cables, UGF,
reverse UGF.
7) were there problems or success?

I'm including some useful comments from Shaji (I'm asking him about his
experiences with potting soil):

> From: "shaji (s.) bhaskar" <bhaskar at bnr_ca>
> In message "re:Aponogeton Madagascariensis", you write:
> >What ratio did you use of potting soil? Was it in pots or substrate?
> >If I used 10% manure or potting soil in a pot mixed with sand, laterite
> >and gravel do you think it would be ok for the fish? I have access to
> >mud from a lake too but don't know how to sterilize it. Boiling? Dry it
> >and screen it to remove insects and twigs? This might be better. Heck,
> >maybe I should just grow my A. mads down at the lake!! :-) (naaa just kidding)
> It was not in pots.  I used it in a 55 gallon tank.  The bottom third
> of the substrate was equal parts by volume of potting soil, peat and
> gravel.  The rest was washed gravel.
> The substrate did go anaerobic ( I could see the bottom of the tank
> darken) for two or three months, but after that, everything was fine.
> Yes, I did have fish in the tank.
> If I were to do it again, I'd probably use potting soil and gravel in
> a 1 to 2 ratio in the bottom of the tank.
> About lake sediment:  Have you considered sterilizing it in your oven?
> 80C for a couple of hours should do the job.
> -Shaji

George Booth had commented that these high organic substrates can go
anaerobic and produce toxic byproducts such as H2S which can kill fish
at certain concentrations. Activated charcoal filtration might be 
effective at removing this I think. (Add the trace iron supplements on
the days the charcoal filtration is not used)

I also wonder how complex a bio system I need in a tank to contain a high
organic substrate. Maybe some of the living stuff from lake sediment might
be a good idea, except for insects, larvae etc. Some kinds of worms might
be highly beneficial or even necessary. It's not uncommon to see micro-worms
in an established aquarium. I don't know where they come from. Don't imagine
the wife will be too pleased however if a batch of mosquitoes invades the
apartment!   ;-)

 - Steve