RE: Lava Rock sand...

["Eric Wahlig" <ewahlig at earthlink_net>]

 I think the lava rock sand, also known as "scoria" ?, has one quality which
should be carefully considered. The texture is very rough or sharp and may
cause two problems as a substrate: Physical damage to bottom dwelling fish
and root damage to plants. Because the grains are sharp, they may tend to
lock together and form a fairly impenetrable substrate. Maybe test some in
a tank where you can observe the bottom glass to monitor root development
or at least run your fingers through it to get a feel for this. I have used
it but only as a filter medium.   

--- Eric