Re: To vermiculite, or not?

> From: Davin Milun <milun at cs_Buffalo.EDU>
> I posted a couple of months back, announcing that I was about to set up
> a plant-centered, CO2-injected 55gallon, and asked for some input
> Anyway, I'm deciding what to do for substrate.  I've been following all this
> vermiculite discussion, and my question essentially boils down to this:
> Of the following list of substrates, which is the "safest", and which is
> likely to produce the "best" results:
> 	1) All gravel
> 	2) A Kelly-Pushak vermiculite/humus/gravel mix at the bottom, 
> 	   with plain gravel on top
> 	3) A mix of just gravel/vermiculite at the bottom, and plain gravel
> 	   on top.
> what I need is basic advice.  I would like my tank to be "successful",
> meaning that it has good plant growth for at least a couple of years.  And
> while I'd like to be able to be another useful data-point in
> net.plant.research, I'd *much* rather be a success data-point than a failure
> one.

I will take as criteria that by success you would like to grow a wide
variety of plants but don't feel the need to experiment with methods
to grow the more challenging ones. We have very many people growing a 
great variety of plants in all sorts of substrates, with or without
UG heating or UG filtering. To be honest, avoiding extremes, the
substrate is not the critical factor. Roughly in order of importance
I would say are 1) adequate lighting 2) nutrient supplementation
3) dense planting 4) CO2 5) filtration 6) water....?) substrate
All of these principles are covered in "The Optimum Aquarium" and
other books as well as here in piece meal form. What we're not saying
here is the relative importance of each of these factors. 1,2 & 4
are important for vigorous growth, 3 for algae control and aesthetics.

The term "safe" is entirely subjective since what we really mean by
that is what is our comfort zone when we take into consideration
our understanding of the scientific rationalizations for why things
work and the trust we feel in methods recommended by various people
and books.

In terms of growth rates, it may be that some substrates are superior;
its just real hard to quantify those differences. Growth rates are
probably not all that important after you get over the hump and
start using the right methods.

I should mention algae control in connection with substrates (lest
George clarify me again ;-) He's saying that with laterite and
heating coils he has fewer algae problems. Let me try to explain
why that might occur. Laterite has lots of iron oxides. In conjunction
with circulation (water flowing through iron oxide) phosphorous
tends to become fixed. Phosphorous is never in short supply for 
aquatic plants (according to jkelly) but excessive phosphates is
considered to be a cause for algae growth. I stopped short of adding
fine steel wool in my substrate but the concept is not outrageous.
I don't know of anyone who's tried it yet; face it, we're all a
little bit chicken. :-)

If you are constrained by your budget, you should not feel that you
are endangering the success of your aquarium by using gravel alone
without substrate heating or UG filtration. In my humble opinion ;-)
you would also be entirely safe using vermiculite mixed with gravel
in the lower layer of the tank. In the Jim Kelly method, you add
just enough water to get the vermiculite wet (not float) just as
when preparing a clay substrate. This prevents cloudy water on startup.
To this you add a few handfuls of ordinary loam. Just enough to
change the appearance of the vermiculite grey. This is plenty. You
only need a tiny layer of the fine humus/clay coating the particles
of the substrate to provide all the CEC you'll ever need. You can
mix this with gravel to add bulk if you need more. Spread it over the
bottom of the aquarium in a smooth layer and then cover that with
a layer of fine gravel. It's probably a good idea to add plant nutrient
tablets after you spread the bottom layer. If you want a deeper substrate,
you can have a layer of gravel underneath the vermiculite layer.

BTW, when Frank was describing his vermiculite/soil substrate
he used equal volumes of soil, vermiculite and gravel. This high ratio
of soil may be what contributed to the slight anaerobic condition
he described. The plant roots however, were white and healthy so,
go figure! Frank also said he wasn't using CO2 on this tank and was
unhappy with the growth but I don't think he was happy with the
substrate entirely because he's replacing it, eh?