Different tank sizes are often quoted for common or singletail goldfish, and fancy goldfish. Goldfish can be divided into two broad types; singletails (often referred to as commons) and fancy goldfish.
Goldfish kept in bowls or tanks that are too small will suffer from poisoning due to poor water quality and internal organ compaction due to a lack of space. These problems both shorten a goldfish's life and stunt its growth leading the misconception that goldfish are small, short lived animals.

The best size tank for goldfish will depend on how many and the type of goldfish you intend to keep.I would also recommend buying a fish that has not come from a community tank and is already used to living in a small tank.

There are other species of fish that can do well with goldfish. But what works and what doesnt work depends to some extent on the type of goldfish you have, the nature of your setup, and the size of your community tank.

This particular example perfectly highlights why Best Tank Size For A Goldfish Community is so captivating.
Goldfish are filthy fish, adorable, but filthy. 5-10 gallons per fish minimum. Double the filtration for the size of the tank but if they're fancy goldfish make sure the water isn't too turbulent. I have my 6 young goldfish in a 15gal with a 30gal pump.
Changing tank size to match the size of your fish is the wrong way to go. Lot's of people do this without knowing that they are harming the fish. A fish will be stunt and you'll never know this because you are keeping it in a small tank.
Goldfish Tank Size: What To Look For. To determine how large of an aquarium you need for your goldfish, you first need to know how big goldfish get. How big a goldfish gets is partially determined by the type of goldfish.