I have been a pond keeper for 33 years, only two ponds in all that time, the first was 1,500 gallons run on a Kockney Koi box filter, I had that pond for 15 years at my old home, when I moved I built a 5,000 gallon pond, bottom drain, skimmer, 2 x returns, Nexus 300 and a Ultrabead 60 UB, I had a home made trickle filter recently replaced by two Evolve 3 tier 1,000 mm showers, I have bread my own fry, and for a few years now I have been growing on 3 week fry from Newforest Koi, I have no idea how many Koi I have, I am probably overstocked, Best Wishes, Anthony from Oxfordshire.