Does anyone have a koi tankI need advise on how to set one up Koi

Many years ago i picked up a baby koi from pesmart.I put him in my 55gal long tank he lived for about 5 years before he passed.I think it was part i kept changing his food i used the tetramin koi pellets.The tank had no heater and under powered filters.Now i want to get another koi and set up the right tank for one and the right food.Any tips?

well darn i will have to use the tank for something else.thank you