My 4000 Gallon, 20x8x4(deep) Koi pond got a major reworking this year. I was having a major leaking problem with the waterfall that I just could not solve. I finally bit the bullet and had a professional pond contractor come and redo the waterfall. Could not be more pleased. Not only could they man-handle giant stones into the design they totally redesigned the waterfall. I'm running a Savio bio falls and a smaller Savio skimmer on the other end of the pond. I learned a lot about what not to do when building a pond, but now I'm good to go. They stripped all of the invasive pond plants out of the bogs (Lizard Tail is evil) and now I have a clean slate. The pond houses 8 koi (mutts), 4 of them are about 16"-20". I'll post some pics of them when the pea green soup clears up when my 36 Watt UV does the job.