I get asked this a lot, usually by someone trying to trim their electric bill: can I shut the pond pump off at night, or when I am away? For a koi pond in season, my answer is almost always the same. Leave it running.
What the Pump Is Really Doing
People think of the pump as the thing that moves the water, but that is only half of it. Running water is how your pond breathes and how it filters. The pump pushes water through the filter where the good bacteria live, and the waterfall or return churns oxygen into the water. Shut it off and both of those stop at once.
Why Nighttime Is the Worst Time to Turn It Off
Here is the catch most people miss. Your pond's oxygen is at its lowest overnight, because the plants and algae stop producing it and start using it up. That is exactly when your fish are most at risk. So the middle of the night, the time people are tempted to shut the pump off, is the worst possible time to do it. If you have ever found fish gasping at the surface in the early morning, low overnight oxygen is a prime suspect.
But What About the Electric Bill?
This is a fair worry, and it usually comes down to the pump itself. An old, oversized, or inefficient pump can genuinely cost a lot to run around the clock. A modern, properly sized, energy-efficient pump costs far less than most people expect to run 24/7, often just a few dollars a week. If your bill feels steep, the fix is usually the right pump, not shutting it off. That is exactly the kind of thing I sort out with pump and filter service.
Winter Is the Exception
Cold months are different. Once the fish go dormant, a lot of ponds get shut down for the season, or switched to just an aerator and a de-icer instead of the main pump. What is right depends on your setup, so it is worth a conversation before the first freeze.
Bottom line: in season, keep it running for the fish's sake, and if the cost is the concern, let me take a look at your equipment. Get in touch and I will make sure your pond is set up to run clean and efficient.