I'm not convinced it makes that much of a difference. For years I ran the diffuser in my trout pond only at night to keep warming down during the hottest part of the summer. At some point i spaced out on turning it off during the day for a few days and didn't see much of a difference. Of course I had well water running in 24/7.

If the water warmed up during the day, mixing with the water at night once the diffuser(s) are turned on, what's the difference if the diffuser is on during the day?

Just my opinion of course and I could very well be wrong.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.