sit down with your goldfish, and find out what they like, they are a very feng shui fish. As for any real solution, our gold fish do the same thing, drive me nuts. We had a tank set up to look like a bar at a mouse perspective, over sized martini glasses and half gallon SKYY vodka bottles, with black gravel and the martini glasses were filled with red marbles (silentSkream likes the cosmos) We had a black moore that would rearrange the marbles by picking them up in his mouth, arrying them to a back corner and spitting them out in a pile.... drove us nuts!