i think if you really want it in there, put it back in. but when i ran my freshwater 75 i had these branch like things that were molds, and they had small areas where fish would go up inside, and either get stuck and die, or just go in there to die. either way, i had a nitrate issue and couldn't figure out why, until i pulled the ornament.
just make sure any holes going in the castle have equal holes coming out. :wink: