Yep, probably the most misunderstood thing or mistake made about "koi" is the size of the pond they require.
No disrespect to anyone, it happens to most of us. It happened to me when I first started 12 years ago. Hey, i wanted a cool koi pond! I didn't know any better! I didn't know those little guys would soon outgrow my (ridiculously small) 300 gallon pond. I rented a machine and built a bigger pond!
The term koi pond is thrown around society without much knowledge.
If I could do it all over, I'd do shubunkin a variety of other goldfish and forget the koi. Don't get me wrong, my butterfly koi are cool, but some of them have gotten huge! Over 2 feet huge.