Heat Pumps are awesome!
Everyone I know (locally) has closed up over a month ago; we're still swimming ( even though we've already been having "frost" at night & the leaves have half changed already)

Being that you're in florida, you could literally swim all-year-round

If you have the cash, I'd go with solar panels & a heat pump.
just set the heat pump to the "minimum" temperature that you like to swim at...
& let the solar panels bring it up to what you really like the temperature to be at ...

Happy Swimming :-)

( I'm so envious... wish I could swim year-round...lol)