I finally got to meet my neighbor, and he showed me his pond. It's small, appears to be about 500 -700 gallons, maybe thirty inches deep with what I would guess is maybe a thousand gph pump and bio filter feeding a small waterfall. There are lots of rocks and plants in it. What I found strange was that there are maybe two to three dozen koi and goldfish in it. The biggest koi is about a foot long and most of the other fish are in the six-inch range. The water is quite clear and it's a gorgeous pond. Isn't that waaay too many fish for such a small pond like that?