I, too, am a koi-aholic. But unlike Grant, I have been koi-purchase-free since this past May. The reason why I have been koi-purchase-free for so long is because I want to be a strict follower of the 1,000 gallon minimum per koi rule. Therefore, I have had 9 koi ranging in size from 15" to 22" in a 8,500 gallon (7,600 gal in pond & 900 gal in filtration) outdoor pond. The pond is filtered by 2 Nexus 300 (each with 150liters of K1 & 50liters of biochips per Jasper Kuijper's rec), one bakki shower out of plastic trays w/ feather rocks for experimentation, and two boxes of J-brushes each w/ containing about 60 J-brushes (I use the brushes mainly as biological). The pond is circulated once every 30 minutes. Here are my water parameters: pH 6.8-7.2, KH 80-100, GH 40-80, & ammonia, nitrite, & nitrate present d/t new pond syndrome.
The reason why I am writing this thread is because I am starting to feel the "craving" to go and buy some more koi. My pond looks so empty w/ just 9 koi in a pond w/ an oval surface area of 21" long and 11" wide. It makes it even harder to follow the 1,000 gal/koi rule when I visit ponds that have "tons" of koi and I speculate that each koi gets anywhere from 200 to 500 gallons. You can't even see the bottom of some of these ponds because there are so many koi swimming around! Granted, I see some ulcerations in some of these koi, but they look impressive nonetheless.
Furthermore, I have been a follower of Mike Snaden's theory of soft water producing massive koi growth. From what I gathered from his articles, it seems that koi do not need a large volume of water as long as there is ample filtration to take care of ambient ammonia, nitrite, & nitrate. Above all else, the water needs to be soft & pH low. And when I say soft & low, I mean a pH the may be in the acid range (6.8-7.4) and a very low KH & GH to the point where you are crossing your fingers and hoping that your water won't crash.
So the question that I would like to pose to all of you gurus is: Is it possible to develop koi to their maximal potential in a water volume that is less than 1,000 gallons per koi? If it is possible, then what are the practices/parameters that it takes to achieve impeccable growth/quality from these koi?