Just a voice of experience here. We also have a two speed pump and a solar heater. We run the pump on high during the day with the solar heater "on", and then turn the pump on low and run it the rest of the time. If we don't need the heater, the pump stays on low. So our pump is on 24/7. I know that might seem like overkill, but we tried to turn the pump off overnight, but were not happy with the condition of the water. Nothing scientific, just our experience.