This happened to me as well, I used normal wood and my aquarium was full with dirt, take the treated wood from the specialized fish shops, they have all kind and forms there without any risk for your fish.

There are woods sold specifically for tanks that are hardwoods mainly from Africa. If you want to avoid the cost of that you can stay pretty safe by sticking to hardwoods from non-toxic trees, such as trees that grow edible fruit. You can also pick up driftwood that is already very seasoned from the river or beach, but in that case you should boil it first to avoid bringing in any parasites.

No no no. Don't use treated wood. Drift wood should come from only some species which is hard and most of tannin had bleached out. Mine, come floating first it came so I have to soak it for more than 2 months before it could sink. You can take home any drift wood you find along sea-shore, or beach line. Give them nice shower, then hot water, soak in fresh water for few weeks, put it in your tank. But please, no to treated wood. I run a wooden furniture factory so I know how nasty chemical used to treat wood.