One of the most important decisions you need to make with your pond is just how much flow you need out of your pond pump. In order to determine the correct size pump, you must first figure out how big your pond is. Grab a tape measure and write down the length of your pond. Then measure the width and finally the depth. Now, multiply the length x width x depth. You now know how many cubic feet are in your pond. Take that number and multiply it by 7.48 (the gallons of water in one cubic foot). That's how many gallons of water are in your pond. For example… my pond is 10 feet long, by 5 feet wide, by 4 feet deep (10 x 5 x 4 = 200). 200 cubic feet x 7.48 gallons = 1496 gallons of water in my pond. If you don't care to get technical, you can just multiply the cubic feet by 7.5 (in my case it only adds 4 gallons).
Now that you know how many gallons are in your pond, you need to determine how often you want to circulate that water. It's recommended that you circulate the water in your pond between 1/2 to 1 time per hour. If you have fish in your pond (which most of us do), you should go on the higher side and filter the water once an hour. Since pond pumps are rated in gallons per hour (gph), I would therefore need a pump rated at 1496 gph or more. I personally use a 2100 gph pump to be on the safe side, but I could easily get away with a 1500. To see a complete list of pumps, click here.
To pick the right type of pond pump (after you decide whether you will use an external or a submersible pond pump), you need to ask yourself what your pump will be used for. Will it be used for a waterfall? Will it be used for a fountain? Mag drive pumps are the most popular because they are relatively quiet, and they're energy efficient. They are generally used for smaller applications. Then there's direct drive pond pumps. They are usually stronger and are better suited to fountains that shoot high in the air or tall waterfalls. Because they're stronger though, they generally require more electricity. Lastly, hybrid pond pumps offer both the benefits of a mag drive pump and that of a direct drive pump. They feature the power of a direct drive and the energy efficiency of a mag drive pump. To see a complete list of pumps, click here.
One of the first things you need to decide when choosing a pond pump is whether it will be an external pond pump or a submersible pond pump. An external pump has the benefit of being easier to maintain (cleaning out any debris that may get lodged into the impeller), with the disadvantage of having excess noise. On the other hand, a submersible pump offers negligible noise. However, when you need to do maintenance, you have to go fishing so to speak.
The submersibles can be relatively maintenance free with the use of prefilters though. It used to be the case that you didn't want a submersible because the seal on the pump could leak sending coolant throughout your pond. We don't have to worry about that anymore with the newer magnetic drive pumps because there is no coolant to leak. Another benefit of having an underwater pump is that it can be used to easily drain your pond. That being said, most people (me included) choose an underwater pump. The maintenance isn't that bad and I personally can't hear it, not to mention that it's at the bottom of the pond instead of in my garden. To see a complete list of pumps, click here.
When the flow of water from your pond pump starts to diminish over time, you're pump is likely clogged up. In order to clean it out, you first need to unplug your pond pump. Next, pull it out of the water (in the case of a submersible pond pump). You'll likely need a phillips head screwdriver and at the very least a pair of needle nose pliers or a pair of tweezers.
What you need to do is clear away all the debris from the impeller. I get snail shells, leaves and various other things stuck between the shaft and the impeller. In the case of a Danner or a Pondmaster Hy-drive pump, you'll need a long phillips head screwdriver to be able to reach four of the six screws. You'll then need to remove the top casing to uncover the pump inside. Then you can clear away the debris with some tweezers.
If you have a Pondmaster or a Danner mag-drive pump (with the six screws visible on the outside), you might be able to get away with just a pair of long needle nose pliers or tweezers. First remove the pre-filter, and see if you can completely clear away whatever is keeping the impeller from turning freely. If you can't, then you'll have to remove the six screws to have better access.
Once everything is cleaned up, reassemble the pump, reconnect the hose (if you removed it) and place the pond pump back in the water (making sure to remove as much air as possible that could be trapped in the hose and the pump). Now all you need to do is plug in the electrical cord and the water should be flowing freely again. Other models are fairly similar to maintain.