Several kinds of driftwood are suited to aquariums. Each kind of driftwood has a unique aesthetic, and many types even effect water chemistry. For the healthiest aquarium, you must pick the right driftwood for your tank.
Malaysian Driftwood
Malaysian driftwood is collected from southeast Asia. The branches have a dark color, with stark, linear shapes. Malaysian wood has a strong effect on water chemistry. This wood will darken aquarium water and lower the pH. This is not nessisarily a bad things. Many fish like tetras and dwarf cichlids prefer tea-colored, acidic water since it mimics their native rivers. Unlike surface wood, Malaysian driftwood sinks in water instead of floating, making it easier to position in the aquarium.
Mopani Wood
Mopani wood may sell under the name African driftwood. This driftwood has some properties similar to those of Malaysian wood. For example, mopani wood lowers pH, though less so than Malaysian wood. If you want to eliminate this effect, you can boil Mopani wood before adding it to the aquarium. Mopani wood had a different look than Malaysian wood, with gnarled branches and lighter coloration. It is another self-sinking driftwood, so you don't have to weigh it down.
Coconut Husks
Pet shops sell the wooden husks of coconuts for use in fish tanks and terrariums. You can buy them with and without the coconut fibers; the only difference is the appearance of the coconut husk. The coconuts are usually halved, which turns them into little caves. These can serve as spawning caves for small fish or retreats for shy species. They have little to no effect on water chemistry.
American Driftwood
American driftwood tends to cost less than other type of aquarium wood. It has light coloration and varies in appearance. However, this driftwood floats. Pet shops usually sell American driftwood attached to pieces of slate or other rocks to weigh it down and stop it from bobbing around in the aquarium.
Planted Driftwood
Planted driftwood is not a specific type of driftwood. Instead, it is driftwood with plants secured to it. Many types of aquarium plants will attach themselves to driftwood. Pet shops now sell driftwood with plants preattached. Java ferns, Anubis plants and mosses are common. These are generally hardy plants that thrive under most aquarium conditions, including low light.
Wood to Avoid
You do have to use some caution in selecting wood for your aquarium. Wood purchased at pet shops is usually safe, but every other source is risky. If you collect driftwood yourself, it could have been exposed to various toxic chemicals, which may leach into the aquarium water. Even wood from the hardware store may contain poisonous chemicals designed to preserve the wood. Some woods naturally contain poisonous chemicals, like creosote woods. Put only wood from a pet shop in your aquarium to avoid risky guesswork.