I've used a lot of found wood in tanks, some with loads of tannins. Ime boiling removes a lot of tannins and does it much faster than soaking. I basically boil until tannins are at whatever level I want or can live with before putting the piece in the tank, which, in my case, means I don't mind some tannin from the wood once the worst of it's been removed. Essentially, I change water in the boiling process until I'm seeing what I want in how much tannin the piece is releasing.
I've also bleached found wood, which is fine but you have to take your time letting it dry to the point where you can't smell any bleach at all before putting it in your tank and may want to do a rinsing soak also-- meaning, again, boiling is the more efficient method.
Ime some types of wood will initially develop a whitish looking fungus or whatever it is, but ime it's harmless and goes away before long, replaced by more normal looking algae, etc. Based on that, my assumption has been that it's an initial stage of microscopic flora in the tank colonizing the wood.