In my opinion anywhere from a 40breeder to a 75g should suffice if it's one of the fancier varieties. If it's anything like a comet I'd say definetly a 40b or 75g or bigger once they pass 8" and move towards a foot. 29s and 55s are only a foot wide and you want to make sure they have room to turn comfortably. A 10" fish in a 12" wide environment is not comfortable. Wide with a decent length and you're set.What is a good size of a tank needed for a single Goldfish?
Right now I have mine in a 29 gallon. I'm not sure if that is big enough since the fish has grown over the past few years.
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