Hi there,
From the links in the last post you will find Marc Weiss products get generally bad reviews.
I did, however, try the black powder (because my LFS owner is a friend and I didn't have to pay for it - ridiculously expensive)
Anyway, my mushrooms did respond to it and after adding it to the water (at a quarter of the recommended dose) I saw bristleworms and small brittlestars coming out of the rockwork. All this means though is that something in it smells good to these critters.
I carried on dosing a quarter of the recommended daily dose, but only every 3 days. Then I got algae problems and stopped using it.
Summary - possibly consists of something nutritious, but not worth the risk since it appears nutritious to nuisance algae too.
Cheers
James