I'd read on the forum that bettas might like to play with ping pong balls, so I picked up a packet at the shops. When I opened them, they smelt of camphor, so I've googled and found that ping pong balls are made of "nitrocellulose, camphor, dyes and other agents". I don't know whether camphor is toxic to fish (not to mention the "dyes and other agents"), so I'm not going to risk using the balls in the tanks, just in case. But I am curious. Has anyone come across this before or know whether camphor is a risk to fish? For the people who've used ping pong balls, were yours made of camphor?