I have to agree CometKeith, I've kept both for many years, IMO Koi are hardier, than a lot of goldfish, Bio load is a must for Koi, they get so big and disrupt so much more that filtering isn't a option it's a necessity. Plants, Goldfish love them, Koi love to eat and play in them! But Goldfish can have their own issues also. The wife and I went looking at fish today, Probably viewed over 1000 Goldfish and Koi. Didn't bring anything home this trip but enjoyed looking. One shop had 6 XXXXXL Sarassa's and Shubunkins for sale, I've never seen 12"+ Goldfish for sale before, and NEVER thought I would be considering $100 for one either. Kind of glad that they were so high as it probably kept me from adding another to the pond, But I have to say, ALL 6 were fine looking fish, I wanted the salt and pepper shubunkin, Literally all white with tiny peppering from head to tell. I need more ponds!!! LOL