I have a pond. During the winter you need to keep an area of the water open so gases can escape and your fish stay healthy. If you don’t do that it’s fish bellies up!
Pond places make gizmos that do that. You can get a bubbler that keeps water moving on the surface so it doesn’t freeze. Or you can buy a de-icer. It’s like one of those immersion water heaters for making a quick cup of coffee or tea but it’s not that hot and it floats on top of a small donut of Styrofoam.
I use both. It’s insurance. I’ve had my pond freeze over and had to haul hot water to defrost a hole. It’s not a fun job.
Until this year, I couldn’t tell if everything was working unless I walked outside (into the cold, cold weather) to look. The underwater bubbler is not visible from the windows and you could never tell if the de-icer was working or not. It only keeps a very small area around it open. I’ve had them crap out in the middle of a cold snap. Bellies up alert!
Fast forward to this year. My new de-icer has a red dot. I can see it from all my pond facing windows. It’s like I’ve died and gone to heaven. No early morning sprints to see if all is good. No frozen butts hauling water. I am very easy to keep happy!
Hope your day has no fish bellies up!