Hi my pond is approximately 250 gallons in the lower, and a 50 gallon preform flowing into the lower pond.
I had just the 50 gallon preform, snuck a koi into it then oops had to make it bigger darn it! After a year in the pond I'm fairly certain he never was a koi, lol too late now. It has a diy biofilter.
I have five shubunkins, three I call the big three, they are four years old while the other two are a year and under. I now also have a butterfly koi who is absolutely gorgeous to me! Found out this year however that Mr Goldman, one of the big three is actually an avid egg bearer. I also have a ton of Texas dawn waterlilies, and duckweed, which I thought they would eat up like every other year, nope not this year.