I'm pretty sure you don't want to mix copper with pool chemicals. I'd use a standard water source heatpump, but have a closed water loop to a stainless steel heat exchanger designed for pool water use. Make sure you get the pump sized correctly for the required flow rate on the heat pump.
The only problem is that water temps will get into the 80's in the summer on the pool. Your effciency and capacity will be reduced a little by late summer.
The energy required to operate the pool feature for added evaporative cooling will consume a fair amount of electricity.