I have re-setup my 55 gallon tank since we moved. This time around I decided to do a goldfish tank. I haven't had goldfish in years. Anyway, what would be a good number of fish to keep in the tank without overcrowding them? Fish being the fancy varieties. Right now, I have two ryukins and two common (I think). I have two power filters and an air stone running. No heater. It's been hanging around 70 degrees.