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Re: NFC: Substrate

Tony wrote:
> Is it absolutely necessary to put some other type of substrate
> underneath the gravel of an aquarium to grow live plants? I've been
> searching for this answer for months now, and still I get mixed replies.

You always get mixed replies because people have lots of opinions on the
subject. :-)

> A local pet shop owner has told me he's ordering some type of special
> matting that lies under the gravel and provides a mess-free base for
> roots to grab onto and receive nutrients. Anybody ever hear of this
> stuff? If so, does it really work? I'm a little dubious about it myself.

I don't blame you. "Snake Oil" is still a mainstay of the Fish Store game,

Gravel alone works, but does not always support really fast vigorous plant
growth. [I love it because it cuts down my hours of trimming and mowing. ;-)]

Adding something with a lot of surface area, and what is called CEC (for Cation
Exchange Capacity), can provide sites for sequestering and slowly releasing such
things as trace elements, including the all-important iron. Laterite,
"Arcilite," vermiculite, plain kitty litter, and good garden loam can serve this
function. The Aquatic Plants Digest discusses (and archives) these topics all
the time. There are pluses and minuses to each, and some precautions to take or
they can be a disaster.

The big things to avoid are too many macronutrients (nitrogen, phosphates,
potassium, etc.) and too much organic matter in the substrate. 

I use a small amount of well-boiled peat between the gravel/Acrilite mixed layer
and the top gravel layer. Keep it well below 5% of the volume of the substrate
though or you can get big smelly belches of hydrogen sulfide gas, and a
chronically sick substrate. I like peat in my tanks, for it has enormous CEC and
does almost magical stuff to the water. If you use too much and it undergoes
"anaerobic" decay (actually oxygen-starved decay), look out!

A plant tank is always out of balance to some extent. Add more light and CO2
becomes a limit. Add CO2 and nitrogen or iron are quickly used up. You *want*
phosphates to be used up, for they are the limiting nutrient for most algae. If
in excess, algae take over.

The trick is to decide firmly what you want from your planted tank. Then
approach getting it in a simple systems-design fashion. Never expect "more" to
be better. Don't mix and match methods until you are a real sophisticate.
Balance light, nutrients and plant selection carefully, and it can be easy.
Substrate additives are just one of those variables that are available to help
you get the effect you want. They are not at all mandatory, IMHO.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntley1 at home dot com

                  Libertarians prefer to do it free!