Thanks for the replies folks.
BBradbury, Dense is certainly one way to describe it! Since I bought a piece distributed and marketed by Zoomed, I can't verify its' source. But the result would lead me to believe Zoomed imports it from Malaysia. May I ask where you got the variety that doesn't leach tannins in such copious quantities?
I fully expected and wanted some tannins to leach out. But as I described, after multiple soaking and boiling sessions, I added it to a cycled planted tank I'm starting and overnight the tank went "lights out". I built the tank myself, so it's 16" front to back and you couldn't see the complete outline of the mopani. Water changes seemed to make it darker, but that's probably just my tainted perception. Now, after a couple of days running Purigen, it's much clearer in there and now it's a matter of dialing in the purigen and leaching to keep it reasonable. Trust me, it wasn't reasonable. The tank resembled a chocolate bar, lol!
I just started converting my SW 125G to FW last night, and I think this piece will just be moved there once that tank cycles. In my 45 or so years in the hobby, I never dealt with driftwood much at all, so I think one issue is that this piece was just too big for this tank, so I'll just move it along at some point to bigger quarters while I soak and boil a smaller piece for this tank. I think that may solve the problem on its' own.
Thanks for the snail suggestions as well. The fungus was a bit of a concern since I was only able to see it for the first time this morning after about 3 weeks in the tank.