I've had goldfish in a regular tank for years and the fish have all lived quite happily for ages with little maintenance. But since I bought a Bio-Orb my fish have started dying with alarming regularity. I've taken advice from the aquarium where I purchased the bio-orb, but it has generally been pretty sketchy and didn't make any difference. The last straw came this week when we emptied the tank completely, put in a new filter, followed the manufacturers instructions EXACTLY, left for 24 hours with the first sachet added etc etc, and introduced ONE small goldfish on Monday. It was dead on Wednesday. Please help!