First off, Mopani wood *is* safe to use in your aquarium.
> Q what the H**L was that stuff!!???
That stuff was simply a layer of decomposing organic matter, plus any
micro-orgs feeding off of it, due to the fact that the wood had a surface
layer of debris that was not removed before being put into the tank.
> Q: should I soak the wood in bleach? for how long? is it safe to use in a
> tank or should I give up about using it? the other piece of wood didn't
> grow slime.
You can, as was suggested, boil the wood, but I would just take a
plastic-bristled brush to it to remove the layer of "dirt." Just remember
to use an "aquarium safe" brush (ie: not one that's been used for
housecleaning!). :-) It will be fine to use, sometimes you just have to
give it a bit of elbow grease. The first one probably wasn't as "dirty."
> Q; should I tear down the tank that I've been conditioning for my G.
> incisus, G. wanamensis wannabees and M .boesemanni and start over again, or
> will a 50 to 75% water change be ok?
A water change certainly wouldn't hurt, but there's no need for anything
as drastic as a complete teardown. Unless it's due for a change anyway, I
don't think you should need to do more than 50% -- it was just some
organic matter after all. My piece of Mopani wood did this same thing. The
snails had a mega feast! ;-) Never a problem for any of the bows, and
they seem to like the tannins that the wood leaches into the water (you'll
notice an amber hue to your water from this).
Hope this helps.
Julie <><