Switching submerged pumps is probably not a big deal. If you already have an unneeded sump pump, I would suggest using it experimentally. You may find that the flow is too small (unimpressive) or too large. From that you could get a better idea for a replacement if needed. One difference between pond and sump pumps is the cord length.

The more critical difference is that pond pumps are generally designed for long continuous running (24/7/365). With energy costs rising, the purchase of a mag drive pump would be the best reason to switch. Mag. drive pumps use considerably less electricity but are more expensive than other pond pumps.

A Flotec Model FPSC3350A sump pump generates 2400 GPH at 10' of lift and draws 9.8 amps of power. $175

A Calpump PW3500 waterfall pump generates 2390 GPH at 10' of lift and draws 4.2 amps of power. $160

Just an example of the difference in energy use. The sump pump is used for getting water that may have debris in it moved fast. That is why they have motors with a lot of torque. Pond pumps are for moving water at a steady rate and are much more efficent. Some sump pumps are oil cooled and could contaminate the pond if it breaks. The pond pump is water cooled and would not pose the same problem.

Matt

When we start to look at pumps the first thing is to forget most sump pumps. They are built cheap and use a lot of power. The reason for this is that most sump pumps run only a short time and the amount of power used is not important. The amount of power that a pond pump uses because it runs 24/7 is important. The Cal pump listed above uses 483 watts or 11,592 watts or 11.6 kilowatts per day. If your electrical cost is $.10 per kilowatt then this pump is going to use $1.16 per day or about $35.00 per month. Then in a lot of places there are taxes based on usage added to this. So the cost to run a pump can run into a lot of money. Yes mag drive pumps usually use less power but they do not fair very well with head pressure. Another thing to look at is how long will the pump last as replacement cost add up. I have no idea how Cal pumps are since they were brought out by Fielding Electric. When Cal owned them they were not a very good pump. The better pond pumps do have oil in them as with the oil they will last longer. The oil is used around the bearings and seals to give far longer life. Submersible pumps are easier to install then an external pump but the external is going to out perform the submersible. They typically use around half the power and last 2 to 10 times longer. As an example a good external that I have uses 289 watts and pumps 4900 gallons per hour at 13 ft of head and it has been running the last twenty years. So the first thing you need to determine is how much water you need the pump to move. Than decide when you want to spent your money either up front or more over a period of time.
Mike

Use the extra sump pump as an auxiliary pump for special clean-out projects.

Invest in a decent but not over-priced mag drive pump. Mag drive pumps are more efficient than most equally-priced oil-cooled from the specs I've seen.

I have mag drive Cal Pumps going on about 4 years and they have performed admirably.

I've kept two running for years and on occasion have mis-treated them, like run the basin dry due to a debris blockage -- either I've discovered it just in the nick-of-time or they've not overheated for whatever reason.

Invest in a quality mag drive pump. You'll save money in the long run. I've got a Pondmaster that is close to ten years old still going strong.

I have used two Pondmaster mag drives(1200 and 1500?) for the past 15 years with no problems. I just replaced them last week with an external pump only because i was tired of crawling on my belie under the waterfall to get to pumps to clean out the intakes. Only had to do this once every other year but it just was not an easy thing to do.