For some reason you don't seem to see many heat pumps here - pretty much all you see is NG. The capital cost for a heat pump appears to be about 2X what heat pumps are. When I go to a Canadian online pool retailer for my 18x36 pool they recommend a 250,000 BTU heater which are about C$2000. For heat pumps they recommend 125,000 which are about C$3800. Any idea what the average operating cost difference would be between the two? Food for thought when I have to replace my ten year old natural gas heater. Any downside to the heat pump, like taking longer to heat up?
I see in your signature that you have evacuated tube solar. Is that plumbed into your pool? I was under the impression those were primarily used for home water heating. I.e. Designed for lower flow, very high temperatures and use an exchanger.
Solar isnt a solution for everyone, but if it is a possibility you might consider a couple hundred square feet of unglazed pool solar panels. They will probably net you far more btus for the money.