Choosing a Pump

The first consideration is external or submersible.  The reasons you may wish to go with an external pump is power consumption and GPH.  Submersibles are easier to install, and generally less expensive, but the most efficient pumps are external. Some pumps can be run as either external inline or submersible.

This is not to say all external pumps are efficient. Many are power gluttons so be sure to check    
Some pumps actually consume less than the rated value.  Perhaps they rate their pumps at maximum power dissipation before failure.  We can only go by the number they specify unless you have access to the pump and make your own measurements.
For example a Max-Flo 960 GPH for $106 will be less expensive at the end of the year compared to an ActiveAqua 1000 GPH for $57.00.
They both pump about the same GPH, but the Max-Flo uses 35 Watts less energy.
That will save you 25 KWH per month if run 24/7.

External pumps generally move more water.   My experience has shown that waterfalls need at least 2500 to 3000 GPH.   Aquaponic systems generally require a pump that match the size of the fish tank.  I've read 2-1/2 times the size of the tank with head loss is about right.  That ratio is probably negotiable.

Head pressure is the height the pump stops pumping water.  Some pumps are designed to move water efficiently with little change in height.  Others are designed to lift water.  You will have to find a pump that fulfills your needs without loosing too much efficiency to lift.  In the comparisons below my calculations for Gallons / Watt are based on zero lift.  Your final decision should be calculated with your required lift in mind.  You will have to consult the head loss specifications which are generally provided. 

If you choose to use a submersible you should be aware that some are filled with transformer oil.  Hardly something you would want to leak into your fish tank or pond.  I've had it happen twice so make certain it says No Oil.  Oil is used to offset the water pressure, and keep it out of the motor compartment.  But there are better ways to deal with this.

Epoxy filled pumps encase the motor winding in epoxy.   The permanent magnet which drives the impeller is allowed to sit in the water.  Epoxy filled pumps are in my opinion the best way to go if you are buying a submersible pump.  Oil filled are OK as a utility pump such as pumping out a flooded basement.

The impeller is often driven by way of a V-notched disk which allows it to slip if it becomes stuck, but the V-notch often becomes worn, and then impeller fails to pump any water at all.  So I try to avoid pumps that use this cheap V-notch clutch.   Other  methods use magnetically connected impellers or direct drive impellers.

Continuous duty operation is important to both a pond or aquaponic system.  The most vulnerable parts are the impeller and the bearings.  Some pumps are designed to allow these parts to be replaced.  Others are designed to be thrown away or the parts are so expensive it becomes a throw away.

Quiet operation is a consideration.  As the bearings wear any external pump will become louder, but it's nice to start out quiet, and when you begin to hear the pump it's time to think about repairs or replacement as it will not be long before it fails. 



Some of the more efficient pumps are listed below.
Submersible pumps in the  700 - 3100  GPH range
External        pumps in the 2400 - 4000 GPH range.

External Inline Pumps
Dolphin 115V Amp Master Series Pump
3900 GPH
161 Watts (24.2 G/W)
 $392.06
ReeFlo 2500/4300 External Pump with Saltwater Seals
2500 or 4300 GPH
105 Watts  (23.8 G/W)
or
4300 GPH
175 Watts  (24.6 G/W)
$299.00
AZFlo 2400/4000 External Pump by ReeFlo
2400 or 4000 GPH
105 Watts  (22.9 G/W)
or
4000 GPH
175 Watts  (22.9 G/W)
$309.00
PondMaster Supreme Inline/Direct Drive HyDrive Skimmer Pond Pump
Saltwater OK
3200 GPH
200 Watts  (16.0 G/W)
$217.82
Pondmaster Magnetic Drive Waterfall/Skimmer Pond Pump
2000 GPH
150 Watts  (13.3 G/W)
$139.00
Alpine Waterfall Hurricane Pond Pump
3100 GPH
175 Watts  (17.7 G/W)
$139.99
CalPump Waterfall Pond Pump
3500 GPH
205 Watts  (17.1 G/W)
$149.00

For many years I  have used a
Sequence 750 Pump 3600SEQ12 -3600 GPH
They seem to last about 3 years which is when the warranty runs out.
3600 GPH at zero head and 2400 at six feet.
They consume 139 Watts  ( 25.9 G/W)
and cost $289.00
 

Submersible Pumps
Laguna Fountain And Statuary Water Pond Pump
750 GPH
112 Watts  (6.7 G/W)
$90.00
Pondmaster Mag Drive Pond Pump
700 GPH
60 Watts  (11.7 G/W)
$94.99
Pondmaster Mag Drive Pond Pump
950 GPH
93 Watts  (10.2 G/W)
$109.99
Alpine Hurricane Pump
3100 GPH
175 Watts (17.7 G/W)
120.00

All but the Alpine Hurricane pump are available at AZ Ponds
I have bought many pumps from AZ Ponds and like doing business with them.
I used to like doing business with them. This last time they failed to send a tracking number.  After I called they said they would call back and never have.  They are on my shit list.

I also have a submersible Alpine Hurricane Pump 2400GPH
2400 GPH at zero head and 1751 at six feet.
The specs show that it consumes 157 Watts  (15.3 G/W),
but my measurements show that it uses only 128 Watts for (18.8 G/W)
It costs $129.00, but I found  on sale for $58.00!
This is a really nice Oil-Free, Magnetic-driven, Epoxy Protected, Ceramic Shaft & Impeller pump with a three year warranty.

Here is another excellent article about pumps.