New to KOI only 5 years with my 6000 gallon pond which is 6 foot deep. It is hot in Tucson so made it deep to keep KOI cool. Also have problems with Blue Herons and bobcats so side walls are straight. We run a massive bead filter good for 28,000 gallon pond. Love to find a Rose bloodline KOI to add to our 12 Kohakus.