From The Aquarium Wiki
Commercial driftwood is dead wood sandblasted to strip off the bark and flakes of loose wood and is then sold in aquarium shops. It very probably has never been in water before so may take time to sink.
Often times, it is attached to a piece of slate sufficiently heavy to keep it submersed, with stainless steel screws.
There are a number of different brands of commercial driftwood sold. These are usually based on where the wood comes from or the species of wood.
Preparing the wood
Do not simply dunk the wood into your tank. Your piece of wood has probably been sitting on a shelf in the shop for a long time. It may have collected chemical sprays from the air and often will be coated with dust.
Take the wood and rinse it under normal tap water and leave it in a bucket of tap water for several days. If the water turns very dark brown then the wood probably hasn't been pretreated and you'll need to replace the water and re-examine the water every 2 days until it shows signs of lessening. This can take months in a untreated piece.
If it is pretreated it should sink rapidly within a day and will not leak out high levels of tannins. Once you're happy with the way the wood is looking, add to your aquarium.
- Boiling wood in water for 6-12 hours is a quick alternative to letting it sit soaking in water for weeks. But this is a very smelly and dirty process for most home aquarists. It also destroys any beneficial fungus or bacteria there may have been on it - along with any harmful ones.
- See bogwood for more detail on the many benefits of using these woods in your aquarium.