NOT KNOWN FACTS ABOUT KOI FISH NEAR ME

I purchased what I thought was a Koi betta - primarily white with a small amount of purple and black. He has absolutely changed colors, and now he is mainly blue and black!koi must be in big ponds 900-1000gallons minimal.. they get large and so are social fish, you critically should rehome that fish, ive acquired a 850gal pond and just after observ