Can goldfish be put in small places?

Goldfish are huge waste producers and for that reason need quite a substantial volume of water. Rules like the inch per gallon rule don't work, and if they did, they could only be applied to small shoaling fish under 2" in tanks over 15 gallons.

Because Goldfish get so large (at least 6" for Fancies, at least 10" for Commons/Comets, excluding tail) they need a big, long tank, tall tanks are not suitable, and they should be very well filtered, ideally with a filter rated for double the volume of the tank.

A single Fancy Goldfish needs a minimum of 20 US Gallons. A single Common/Comet at least 55 US gallons (or a 600 US gallon pond is better!).

Don't underestimate these fish, they may be common in pet stores and sold for ridiculously cheap prices, or even given away, but they are actually very high maintenance and expensive fish to keep properly, not to mention they should live over 15 years!