Thanx for your advice. I do try to keep the tank as much nitrate free as possible ;-) I think you are right on the bladder probelm. The Goldfish tends to have the problem after a meal (sinking food or not ;-) I feed them fresh plankton every so often and the problem is alaways there. I am glad, however, the Goldfish has learned to live with it and is still alive and well - still floating on his back at the top a lot of the times ;-(