The only ornaments there should be in a goldfish tank is solid ones. Hollow
ones dont get air circlation in the ornament and you wind up with stagnat
water. This can result in bacterial infections, this isnt a possiblity if the
ornament isnt cleaned out at least twice a week, this mean taking it out of the
tank and cleaning it with some type of wire brush inside. I really stress this
to everyone. I had an ornament my self for many years and had three fish die of
dropsys before I really knew what was causing this in my tank and to my fish.
If you want things in the tank I do Strongly suggest natural things in there
This is a photo of what I mean by hollow ornament.