So you'll want to avoid Pine, cedar, and fir as they definitely are not suitable for aquariums due to toxic phenols that can harm fish if they leach into the water. Any other wood thats collected from your yard needs to be fully dried.
Wood from fruit trees such as apple, cherry, and pear is generally safe for aquarium use, but if its still bendy after drying it indicates sap presence, which will be harmful.
Safe woods include: Alder, Apple, Beech, Birch, Cherry, Hawthorn, Heather, Oak, Pear, Sycamore
