Aquarium Wood
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Aquarium wood, also called aquarium driftwood, adds a nice decorative touch for many aquariums. Adding aquarium wood makes an aquarium look more natural and can also help create a more biologically natural environment. Wood is a natural part of many natural aquatic habitats where fish live and can be a host to beneficial bacteria that will colonize on the wood. It also makes great habitat and hiding places for fish and other animals.
Care should be taken when selecting wood for an aquarium. Unlike most natural habitats, an aquarium is a closed system where chemicals in the wood are unable to flow away. Wood releases tannins into the water which can reduce pH and color the water. Some types of wood release more tannins than others and with some aquarium woods it can be enough to harm fish although in most cases a little tannin in the water is harmless. With black water or Amazon themed tanks, the colored water is actually desired.
The way to prevent wood from leaching too much tannin your aquarium water is to first soak it in water for a while. Keep changing the water every few days and notice how the water becomes less colored over time. With some types of wood, a couple weeks is enough, some may take a couple months for most of the tannins to leach out. Keep in mind that you will not remove all the tannins but after soaking it for a while any leaching will be at such a low level that it will not be noticeable or harmful.
Some people like to soak their aquarium wood for around a week and then just use carbon in their filter to remove the tannins. This does work but keep in mind the carbon will also remove nutrients in the water that are valuable to aquatic plants. You will also have to change the carbon filters often, which can be expensive.