My neighbor (sadly) is dismantling her 7,000g koi/goldfish pond. She has several neat fish, but she has this one beautiful comet. It's completely white (pinky-white) and it has long, flowing fins. I would say that not including the tail, it's about 6-7 inches long. A while back, I promised myself I would eventually get a goldy tank and now seems a good time. I have an empty 37 (same footprint as a 20L or a 29, just taller) and I have yet to set it up. I would overfilter it. If it really did get too big, I could put it in our pond, but I want it indoors.