Technically, you probably could just turn off the fan, but why not just close the valves at the same time and avoid wear and tear on the sump pump? I have mine programmed so that it turns on/off at specific times. When turned on, the actuators open and when off, they close. But they’re not temperature controlled. The Glacier isn’t really conducive to that, as it takes quite awhile to cool off the water and rarely gets so cold that I’d want to shut it off. Instead, it does a very good job of maintaining temp at a comfortable level, but not constant. My water temp can start the day around 80-82° but will only rise to 83-85°. And that’s running the chiller 3am-8pm. The only time I shut mine off during the summer is during extended periods of rain, like we just recently had. Mine has been off since 7/3 (83° was too cold for granddaughter), but turned back on today.