I have a 1,300 gallon koi and goldfish pond. It is 20 feet wide, 13 feet long, and 2 and a half feet deep. We were going to make it deeper but realized there were some pipes... oops lol. My advice is to make it as large as as will fit and feel nice in the space. You'll be just as sore from digging out 2,000 gallons worth of dirt as 1,000 so make it as big as possible!1000 gal goldfish pond
or a 40g fancy goldfish tank
if someone helps me take care of it