large pond .. Should I turn the pump off?

Here's how to find out how much your pump's electricity costs:

Amps x volts divided by 1000 x KWH cost x 24 hours-a-day x 30.4 days- per-month = cost per month.

I suspect electricity where you live costs more than water.

But I would leave the pump running regardless. It's best for the fish.

You have a few issues here.

Your water that leaves when it's turned off - that's part of what's called your 'water in transit', the problem part is what can't be contained by your lower vessel when turned off. A surge tank can remedy this, as can other solutions - but I'd have to see it. Leaving it on 25/7 can eliminate this effect - until someone has to work on it.

Off or not - if it is a sterile pond, you may only need 4 hrs a day for the sanitization, if your circulation is proper. If its a single pump setup, then override the timer to get the look (if you have a waterfall or fountain) when you want it.

If it's a live pond, then it really needs to run all the time.

These points are all part of a proper waterfeature design. Unfortunately, in this market, lots of folks and others are creating things which have the attributes you describe - and plenty more.

It's like the professor of Landscape Architecture at the University of Arizona said, 'A waterfeature that is not properly designed and/or built is a planter waiting to happen'.

Good Luck!

If I understand your question, you should be able to add a valve to the line so that the water does not drain(you would have to turn it on and off ever day). You can leave the pond running 24/7. Most ponds that we have built run 24/7. If you have koi in it, it is good to have it run all the time anyway. Depending on the pump, the price of electricity, and how much water you are having to add every day, it might be better or not. If the pump is out side the water(external) you might have issues with priming the pump every time you shut it down. The pumps can handle being on all the time, but like everything in a pond, they will need maintenance.

-as for the electric vs power-trial and error.

-Find your local Pond store, and become good friends. They are usually full of good free advice.

It will actually shorten the life of the pump to keep turning it off as sediment can settle in the bottom of the pump and screw it up over a little time. Leaving it running uses very little electricity.

You should never turn off your pump. It will lead to other problems including cloudy water etc. They are made to stay on all the time. It doesn't use that much electricity.

Water is less expensive than electricity.