This has been posted on "Planet Catfish" as well <View topic - Little help>, my thoughts were the same as Ed's (probably Cupressus macrocarpa), but looking at the bark and wood colour it might be Plum or Cherry (Prunus). You can see prominent horizontal lenticels on the bark.Looking at the widely spaced growth rings and the compact root ball with no major tap roots I'd say that wasa softwood stump (probably a pine or cypress) and I wouldn't use it submerged in a tank personally. However you could soak it and see what happens if you really like the shape.