The stuff on the grape wood looks like biofilm or something, I used to have something like that on my driftwood but my nerite cleaned it off in a matter of weeks.
5 to 10 years
When was that grapewood added? If its newish, its just some harmless, filmy stuff that develops on newly added driftwood. Some fish and snails find it delicious. If nothing will eat it off and it bothers you, you can always just scrape it off.