While the goldfish bowl of old may not be enough, I think 55 gallons is just a wee bit of overkill for 2 fancy goldfish 8O. Everyone should agree with Louise, regular water changes, while not always the end all - cure all, are a necessity. The closer, chemistry wise, the new water is to the old water, the less stress this will put on your fish. You really want to dilute the toxins. Repeat after me - "dilution is the cure for pollution"
Then again, maybe it's just your fantails' time