Is it possible to add and control a booster pump on a DualSun pool heating system?

Yes, with a DualSun SLL solar controller.

Here is a diagram that explains how to wire and control the booster pump:  

•  Press and hold down the button

  

• Turn the rotary actuator to the desired menus

• Enter the menus by pressing the button

  

• OPARR = ON

• REL = R2

• RELR = R1

• INVERS = OFF

• Relay R2 = ONOF

Example of contactor model: Relay 230V - 2 NO contacts - 9A (AC3) contacts for inductive loads (motors, up to 1300W).