Since my ponds are for waterlilies, I have no reason to constantly monitor water temps. I let the plants tell me when the water is warm enough to start the growing season or cold enough to bring it to a close.
Years ago, I was breeding & raising Koi. Water temperature was much more important to me. But of all the critical water parameters, water temperature is the slowest to show a significant change.
From a design standpoint, a dedicated Koi pond is a complex system. Every thing added to that system is also an additional potential failure point. Especially so when the addition is an automated one with its own internal complexities. This is why I've always been an advocate for design simplicity.
That said, I'd not argue against having a water temperature monitoring system, as it would be one who's failure would be the least likely to result in a catastrophic system collapse. But I would consider it to be a "nice-it," rather than a necessity.
Just some rambling thoughts brought on by your post.
Mike S.
Spring Hill, FL
