Would it even be possible to heat an outdoor pond in MA in the winter? like a thousand gallon blowup pool or something?
Possible of course.....the cost would be crazy. You would be much better off having it below ground as mentioned.....4 feet deep minimum in these parts. Keeping a pond for koi around here is not real hard. Tropical fish would require a crazy heater....think Jacuzzi size. if you can keep a Jacuzzi outside 104 degrees in winter why not keep 78 degrees with a similar system
Anything is possible but why? I would either go with a temperate/cold water in ground pond or get a monster tank inside.