Hi all... I live in the great northwest and have had our pond for about 1 1/2 years however, our first attempt was a very small (300 gal or so) and the people who put it in said we didn't need a filter 
Well we quickly realized that was wrong so this year we went somewhere else and had our pond enlarged to about 1000 gal w/ a filter, waterfall, stream and bubler rocks. Had 4 koi in the small pond for a year but once it was enlarged we must have peaked the interest of the most unfriendly heron and within 3 weeks we lost all four. We now have a heron statue, which we move every day and a scarecrow water sprinkler. So far so good. We have put in 3 goldfish (so as not to go broke feeding the heron) and we are keeping our fingers crossed. Algae was always a problem, but with the filters seems to be doing better. So, not too much experience, but we are learning. Looking forward to checking out this site to see if I can get any other pointers that will help.
Well we quickly realized that was wrong so this year we went somewhere else and had our pond enlarged to about 1000 gal w/ a filter, waterfall, stream and bubler rocks. Had 4 koi in the small pond for a year but once it was enlarged we must have peaked the interest of the most unfriendly heron and within 3 weeks we lost all four. We now have a heron statue, which we move every day and a scarecrow water sprinkler. So far so good. We have put in 3 goldfish (so as not to go broke feeding the heron) and we are keeping our fingers crossed. Algae was always a problem, but with the filters seems to be doing better. So, not too much experience, but we are learning. Looking forward to checking out this site to see if I can get any other pointers that will help.