I run my inside pond during the fall winter and spring at no lower than 53-55 F. Then with the approach of spring I start cranking it up. It's 64 F now. I don't experience a temp alley
(always listed before as 55 to 65 ) because of the attention to water quality. My indfoor pond is tiny and crowded ( only half the size of my outside pond ) but I've never had issues, which in my mind confirms what's been said earlier by Mike and Jim.....