I agree with all the advice and commentary above. To add some perspective, I have a similar sized pond, at 1200 gallons (approximately 4500 liters) with a 3x6 foot, 1 foot deep bog (thanks to this group) in Florida US which has a long hot summer. I have 1 koi and 25 goldfish (were 3 goldfish a year ago; baby goldfish available for a new home!), and I don't see having more than the single koi in my pond, based on room for him to swim freely (the goldfish learn to stay out of the way or merely follow him around).
My previous biofilter could not keep up with the fish load of a koi and 3 goldfish, despite weekly filter changes, bi-weekly water changes, and plants in the pond. So I built the bog, finished it in late summer, and my water clarity and quality improved within days of going live. The final test will be in the height of summer, and I am sure I'll be adding aeration to supplement the waterfall oxygenation.
Good luck with your pond.
Hi, SarahT! I ran across your reply to the full medical pond report by Pineapple and see that you also have a 1200 gallon pond here in Florida (I'm in Daytona Beach). I inherited a sludge-filled abandoned pond five years ago and rehabbed it. Previous owners said "water birds" took all their fish and got tired of it. In five years I haven't lost a single fish to predators of any kind (although I myself killed several fish early on due to forgetting to turn off tapwater - have since put a timer on the faucet, duh, and also built a rainwater collection system). A green heron landed in my yard while I was still digging out the pond, and I found raccoon footprints in the sludge. Later, when the pond was on line, I found neighborhood cats staring at the fish intently but not willing to get wet.
Of all the advice I have read about ponding on these threads, the most significant was in one word: Patience.
Most of the other advice reflected the individual experiences of veteran ponders and I have found my own experience to be significantly different at times. For example, this oft-quoted formula of "1 koi per 1,000 gallons" I find to be quite puzzling, as I purchased a half dozen koi fry, a half dozen comets, and four plecostami when I initially stocked my pond. The pond has two adjoining 600 gal sections connected by a sluice, and I separated the comets from the koi and split the plecostami. I used a Pond Guy pump and pressurized filter along with a filtered skimmer and its own pump circulating through three spitters. Never had room for a bog filter, but weekly backwashing of my UV pressure filter has kept the water crystal clear. Using 70% surface coverage with water lettuce has also helped to keep organic nitrogen, ammonia and phosphorus at zero concentrations.
Over the next year (three years ago) the fish grew, as they are wont to do, with one koi becoming an alpha - it grew to a foot in length, followed by the others in lesser increments. Wherever the alpha went, the others followed in formation. Of course, in an 8-ft x 5 ft pond section (28" deep), a foot-long fish can't go far without having to turn around! Now, I suppose some fish lovers would object to confining a big fish in a small pond, but this alpha (he's orange and white and I call him The Creamsicle) seems happy, as do his smaller kin. In fact, the largest black koi (6") managed to produce three black fry to my complete surprise. At this point, all the fish - including the comets in the "upper" pond - have stopped growing. Even the small ones. The plecostami, however, tripled in size! They look like sharks, cruising along the bottom, mostly coming out at night. I did lose a comet to "suicide" - he jumped out of the water and landed on his side in the sluice, and even though one gill was under water, it wasn't enough (I was able to rescue another comet two years ago when the same thing happened).
Last spring I had some green algae problems, which didn't bother the fish much. In fact, I cut back on their food pellets when it seemed they weren't hungry, and then I wound up not feeding them at all - for months! They apparently turned to eating algae and stripping organic material collected in the water lettuce roots. This regimen helped clear the water. I added more filtration to the skimmer as well as backwashing the pressure filter daily, using my Bluebarrel rainwater system to replace lost water.
For the entire summer, the pond did well, staying crystal clear. I've had string algae growing on my two waterfalls as well as the sluice, but I accepted the fact that the best way to deal with it is manual removal, which takes only a half hour every few weeks. As you are aware, temperatures were not that bad here while the rest of the country sweltered and burned. I let the water lettuce, which grows like mad, cover the entire surface of the pond to give the fish shelter and keep temperatures down. Now, with the sun lower in the sky and temperatures dropping into the 60s, I've removed much of the water lettuce and resumed feeding the fish, only with a lot less food, hopefully to keep them picking at algae growing on the sides and under the waterfalls.
So, long story only a little shorter, my point is that a half dozen koi and comets (plus plecos) can be perfectly healthy - for years - with a whole lot less than the 1,000 gallon minimum per koi that the experts claim is necessary. Anyway, I'm not impressed by two-foot koi: At that size they begin to resemble their not-so-attractive cousins, the carp.
