lots of south american fish enjoy blackwater conditions, i add blackwater extract to 2 of my tanks since the wood has stopped leaching. there are other nicer woods out there from companies like ADA but they are tough to get and insanely expensive. overall i prefer manzanita for its crazy branches and color or malaysian for a darker look
I've been shopping for perfect driftwood for a tank I'm working on setting up so I thought id share what I've found because I'm super picky and pretty sure I found the end of the Internet searching for the right driftwood and those were the 2 places I kept coming back to.
I'm sure you could probably find something locally. Just keep in mind some woods will sink automatically on there own like malaysian. Manzanita will sink after given enough time to water log itself. Tying it down to a rock keeping it entirely submerged will speed up the process by maybe a day or two. Not sure how mopani is never tried that kind.
Tannin's will leak out of all types of woods some more then others. Boiling as stated by another user here will help reduce the amount that leaks. The hot water forces it out so if you got a warm water tank it will leak more then versus a cold water goldfish setup. Manzaman has some awesome pieces. I have bought many pieces from him.
I screw mine to a piece of slate with a stainless fastener. The tiles I get are 12X12, and about 1" thick. I just break them up with a claw hammer, and they drill very easily.