I agree that it needs to be hard wood. I live near a large lake with lots of drift wood on its shore line. I have collected my drift wood, which is in my aquarium now, from this lake's shore line. When I find a piece I like I test how hard it is by tapping on a hard surface and if it splinters or brakes I throw it away. If it holds up to being hit I then scratch with something hard like a spoon, I don't use something sharp like a knife. Sometimes the outer surface is soft but underneath it is good hard wood, so I clean it up, boil it and use it. My BN plecos love this wood.