from itsafishthing.com
For common goldfish or single tail goldfish, each fish should have between 30 and 40 gallons of water, with fancy goldfish being able to do fine in 20 gallon tanks.
Therefore, what tank size is ideal is going to depend on the specific species of goldfish which you have. However, generally speaking, the bigger the better.
For common goldfish, a 40 gallon tank is fine, and you’ll want to add around 10 gallons of tank size per extra fish, with the same being true for other types of goldfish too.
still not right, but IT IS FROM THE SAME WEBSITE....
i feel like the people have different opinions operating the site