Koi ponds are a lot of fun but be prepared for a lot of strong opinions of how best to set one up - especially in Cali. Lots of super nice ponds out your way and big dollar fish dealers.
Here is a pic of my setup - 3600 gallons, 20x15x3 kidney bean shape, epdm 45 mil liner, two 3 inch bottom drains, Aqua Ultraviolet Ultima 4000 filter with 2" head, Sequence 6000SEQ23 External Pump, Aqua Ultraviolet UV Light 80 watt and a big air pump for a couple airstones in the pond.
Some things I learned the hard way are -
-have to have bottom drains and make sure the bottom of the pond slopes toward them
-pump/filter capacity to turn the water over every 2 hours
-at least 3 ft deep with straight sides to deter predators
-uv light a must for clear water
-don't buy too many fish
