The strange looking slimy stuff actually had a web-like or lattice-like structure or pattern unlike anything I'd ever seen in my tanks before, and it shifted every few days by a cm or two. It actually took me a week or so to realize it was shifting. The driftwood was well-seasoned so I was surprised to see that much growth explode on it. My concern really was what else could be promoted to grow if all that was. The tannins were too much. It was capped by an inch of sand or a slight bit more, my standard that I've never had a problem with. It was dark enough that if I held my hand on the back side of the tank I couldn't see it. Even after a bunch of 100% water changes over a couple of weeks the water would get like that in a few hours. You could actually see the color just seeping up through the sand. I like the way tannin-stained tanks look, but I like to see my fish, too.
I agree that there may be not be anything inherently problematic with mushroom soil in general. Common sense and basic understanding of soil leads to that conclusion. What I had may not have been the best stuff in general though. It was just one of those gut feeling things that I should scrap it. I'm sure you've had those gut-feelings, telling you something isn't right even though experience tells you it should be. This was one of those instances for me.
WYite
