In a word, yes. If your pond contains fish or other live animals, the water needs to be circulating 24 hours per day. Even a few hours’ pause can be damaging to your tiny ecosystem. As the water becomes depleted of oxygen, bacteria and microorganisms will begin to die, releasing ammonia and other harmful compounds, which in turn exacerbates the lack of oxygen to your fish. If your pump’s filter dries out, you’ll lose the load of beneficial bacteria that process waste. Dealing with the poisons from stagnant areas and waiting for a new bacterial colony to become established are risky times for the fish and other inhabitants in a pond, requiring frequent water testing and balancing. Breeders of koi and other valuable pond fish usually keep some sort of backup generator or even a UPS (battery backup) with an emergency aerator or pump to carry their ponds through crises like power outages. This is serious stuff!
If your goal is to save on your electricity bill by turning off the pump periodically, you’ll lose more in fish death and maintenance issues than you’ll save. Pond pumps used to be quite inefficient to run and could eat up a considerable portion of the household electricity budget, but technology has progressed, and now pond pumps can cost as little as a dollar per day to run, or even less, depending on the size of your pond. Check the wattage on your pond pump -- you can use a simple online calculator to figure the monthly cost of operation running 24 hours per day. Chances are, you’ll realize it’s a much better strategy to keep the lights on.
