did you try boiling it.... sometimes that helps, though I've never been able to have a piece small enough to fit in a pot..... Are you weighing it down in the tank? I had a piece that I had soaking in a large bin and after 3 weeks, it still shot to the surface. What I did was, I went and got 3 big rocks, sat them on the edge of the slate that the wood was anchored to and sat it there like that. It's been quite a while and that thing still is a little wobbly if I remove the rocks.