sorry to hear that Joe.. Hope things get better very soon
We have two different heaters, currently using the raypak 155,000 BTU unit on the quarantine outside. Long term, will not be using it, as there are many issues I don't like about it (can go into more deep if need be), but it does work for now. Also have one (will need two for the big ponds when done) larger Koi Heat heater that I used at the old house for a while to test it. it works well, after a few minor adjustments. Just was over kill for the 2400 gallon quarantine for now, so we hooked up the Ray pack for now.
Temps are varied throughout the year between 75-78F to 52-55 at lowest. I shoot for 55, but sometimes in a real cold snap, it can overwhelm the heater a little bit. I think the 20F difference is important.
If I had to start again from scratch, would either buy the one from Koi Heat or USA Koi that is similar. Sized according to need.