From what I understand, the basic stocking rule for gold fish is 2 gal. of water for every inch of fish.
I don't think a 20 gal. is too small unless you're getting something like Kois which are pond fish.
That breaks down at the low end of the scale. Goldfish will easily hit 8+". So in theory one is fine in a 20 gallon using the 2"/gallon rule. But if you accept that logic a 4 foot arowana is fine in a 55 gallon tank as well using the standard 1"/gallon rule (despite being unable to move).
I don't think standard goldfish should be kept outside of a huge tank (and who would spend the money for a huge tank for goldfish), or in a garden pond. Really, they can be better, and prettier, than koi. They just don't have the price tag.
I don't think a 20 gal. is too small unless you're getting something like Kois which are pond fish.
That breaks down at the low end of the scale. Goldfish will easily hit 8+". So in theory one is fine in a 20 gallon using the 2"/gallon rule. But if you accept that logic a 4 foot arowana is fine in a 55 gallon tank as well using the standard 1"/gallon rule (despite being unable to move).
I don't think standard goldfish should be kept outside of a huge tank (and who would spend the money for a huge tank for goldfish), or in a garden pond. Really, they can be better, and prettier, than koi. They just don't have the price tag.