I have a 55 gallon outdoor pond. I want to get two small koi. Will this be big enough?

I am confused on this because at Petsmart the details on the tank with the small koi say Tanksize: 30+ gallons. However, when I do searches on yahoo it looks like everyone says 1000 gallon ponds or bigger. Why would petsmart say 30+ gallons, if 30 gallons is too small? Are there different variety of koi that would make a difference? I notice one tank said 30+ gallons then another tank with koi said 50+ gallons. It is confusing and the person working there was about 18 and had no clue.