[censored][censored][censored][censored] man. Anyone knows where top fin makes their stuff?!!Hi Xavier10,
If the ornament is wood it could be fungus; unattractive but not a major issue.
If the ornament is metal (or painted wood) then it could be lead hydroxide. A lot of ornaments made in China contain lead and China is notorious for using lead-based paint. Of course, lead (or any heavy metal) is not good for the fish in our aquariums.