Re: Soil Substrates, Gravel or Laterite

["Eric Wahlig" <ewahlig at hotmail_com>]

Regarding substrate compositioin, Rich asked:

>Has using a soil substrate gone out of fashion, or have people found that 
>gravel & laterite is better?

In my opinion, neither one is better than the other. Or, more correctly, one 
may be better than the other depending on your purpose and expectations.
To help aid the following discussion, the term "soil" is so generic that it 
really can't be used alone as a description. Laterite is, itself, a type of 
soil. So, technically, if you are using laterite then you are using a 
soil-enhanced substrate. Soils vary infinately in composition throught the 
world. Even "potting" soil or "garden" soil does little to provide an 
identification or standardization of the "dirt" we use to grow plants.
This makes it very difficult to prove that "X" soil works well or not. In 
fact, "X" soil may work really well for one aquarist while it causes total 
disaster for another. But, through experimentation and statistical 
evaluation of a large pool of data, trends and general correlations can be 
observed.
An important characteristic of soil, as used in the context of aquarium 
substrates, is it's degree of "lability", or chemically and biologically 
reactive potential. Highly labile substrate compositions have a higher 
percentage of organic content (and probabably microbe population as well). 
This can lead to significant biological and chemical interactions within the 
substrate when it is submerged. A substrate with a relatively high lability 
is sometimes necessary to grow certain "difficult" plants. It provides an 
abundance of nutrients both micro and macro. However, it's high libality 
makes it potentially disasterous if the aquarist is not in a position to 
effectively understand and deal with a variety of rapid and large, the 
gravel/laterite method provides a substrate that can function well over a 
wider range of parameters or tank conditions than a substrate composed of a 
"soil". This is because It's less labile, or "rich" than a substrate 
containing a soil










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