Got my 16 Nishikigoi now sansei, they are swimming around in 22 degrees celcius at the moment, but covered up with polycarb sheeting as its only 10c outside air temp.
3Kw in line electric heater, 220w UV water steriliser/clarifier, 640 litres of water in the filters with Japanese matting cartridges self built in the style of an Eric 4 filter, mines a bit bigger again self built. Pond is built from concrete block 7N dense blocks (20kg each) built on concrete base 3 cubic metres poured, insulated with kingspan rigid foam foil covered sheets 6 inch thick or 150mm, fibreglassed and top coated n black, top of pond is finished with Indian stone for copings, block work rendered and painted. Pumps recirculate the full 10,640 litres or 10 ton or 2240 gallons every hour through filters, second pump runs skimmer line, 2 air pumps 120 litres / min to filters and a 80 litres per min to aerated bottom drain.
Koi nerd talk pmsl.