Looks like there is an optional rapid heater for these things,
requiring it's
own separate GFCI circuit, in addition to the circuit for the pump.
First, I'm wondering first if the heater is a must-have kind of thing.
That is, isn't filling it with hot tap water enough? Or perhaps
it depends on how long you plan to sit in it, since the water will be
cooling down.
Second, why is a second circuit needed?

TIA

Ed