Onyx Sand vs Gravel and Laterite for Discus?

["Jen Jones" <jen.jones at tufts_edu>]

Hello everyone -

I'm a long-time lurker on this list, but rarely post.  I appreciate all the
info I've gotten from this list!  I have had plant tanks for several years,
and am interested in setting up a planted discus (120 gallon) tank.  I'm
_not_ interested in breeding the discus (no time) - this tank will be my
first experience with them, but I've kept tropical fish for almost 20 years.
My tap water tests at 0 degrees GH and 1 degree KH with my test kits.  I've
used fluorite in the past, but wasn't happy with it because I find it
difficult to root plants - I prefer the consistency of fine gravel as the
substrate.  I mentioned my intentions to a pet store employee, who balked
and basically refused to sell me the onyx sand because he was convinced that
my water would be far too hard for discus.  My intention was to artificially
raise my water hardness to around 5 degrees with RO right, etc anyway, as
I've read several articles on the krib and the back issues of this list that
make it seem like this would be fine.  My intention is to go with the theory
that if you set up your tanks successfully for plants, the discus will do
just fine.

That was a long intro to my questions:  Does anyone have any experience with
Onyx Sand, and what does it really do to your water hardness?  Should I go
the safe route and just stick with gravel and laterite? (And does Onyx Sand
look as cool in the tank as it does in the bag? :) )

Thanks in advance for your help,
Jen