Oak is a classic wood and oak leaves are often used in aquariums. But does that mean you can put an oak branch directly into the aquarium?
The answer is: sometimes, but with caution. Oak can work if it is properly dried, untreated and from a safe place. Fresh oak or unknown wood, on the other hand, is not a good gamble.
Why oak can be interesting
Oak contains tannins and can contribute to a more humus-rich, natural feel in water. Oak leaves are often used in shrimp aquariums, blackwater aquariums and biotope-inspired aquariums.
Old oak parts can also be beautiful and hardy. In some cases, oak can become very dark and stable after a long period of exposure to oxygen-poor peat or bogs. This is called bog oak or bogwood, rather than a normal fresh oak branch.
The problem with fresh oak
Fresh wood contains more easily degradable substances. It can start to decompose, produce deposits, affect the water and create a messy start-up. If the wood is still green, pliable, has a strong odour or fresh bark, it should not be used directly in the aquarium.
Care should also be taken with wood from places where there may be pesticides, traffic pollution, oil, salt or other influences.
Bark, rot and unknown treatment
Bark can drop, collect dirt and decompose. Some aquarists use bark, but it requires care. For most people, it's safer to use material that is already designed for aquariums.
Never use oak that has been varnished, oiled, impregnated, painted or treated. Boiling does not make treated wood safe.
Oak compared to Tuskwood
Tuskwood is not a random oak branch from the forest. It is old bog wood from Nordic peat bogs, selected, cleaned and sold as aquarium rot. The material has already spent a very long time in an environment where decomposition has been slow.
It makes Tuskwood more predictable than collecting oak yourself. You get a root selected for aquarium, with dimensions, images and WYSIWYG form.
In short
Yes, oak can be used in aquariums under the right conditions, especially as leaves or very well dried, safe wood. But fresh or unknown oak is not something I would recommend as an easy solution.
If you want that dark, old, humusy feel without taking chances, real bogwood like Tuskwood is a safer and more practical choice.