Which Pump Do I Need?

     Choosing a pump should not be a difficult task, but it is something you should invest some time and research into. We have come up with the following information to help you in making this decision. One point we would like to make is that all of the components in your water feature work synergistically. If you skimp in one area like the pump you may end up paying for it one way or another in the future.  This may manifest itself in a pea green pond or the loss of livestock due to improper flow through the bio filter.  Or, that majestic waterfall you have envisioned all winter turns out to be more of a water-drip than fall.  So take your time and if you need any more assistance feel free to contact us, we are always glad to help!

Biological Filtration

     One of the most important parts of a pond is the biological filtration.  Now most people opt for some sort of external system.  The minimum rule-of-thumb is to move half of the water features volume (this includes waterfalls, streams, ponds, etc.) through the filtration system per hour.  For example if you had a 9’ X 12’ pond with an average water depth of 24”, you would have a volume of approximately  216 cu ft. which is 1,615 Gallons.. Therefore you would want a pump that would move a minimum of 800 gallons per hour. This would be the minimum for the whole system, meaning we have not taken other factors into account like head loss and  friction loss, or flow rates for skimming the pond using a PSA skimmer, which we highly recommend (located under skimmers).

Skimming Considerations

     When using a through-the-side skimmer (such as the ones under the skimmers page) to obtain the best skimming action you will want a flow rate between 10 to 15 times the ponds surface area in square feet. So for the 9’ X 12’ pond in the example above, you would have 108 sq. ft.  Therefore you would need a pump that moved between 1080 to 1620 gallons per hour.  Larger pumps would provide more aggressive skimming for oddly shaped ponds or those with heavy tree/debris loading.  If you have a very large pond, another solution would be to use two or more skimmers each with their own pump.

Head Loss

     Before you can pick a pump for your pond you, need to determine the flow what flow rate and total dynamic head (TDH) you want. Since the flow rate is affected by the head it is working against, you mist know both parameters to properly select a pump.

Flow

   The exact flow rate you will need depends on many factors including the size of your pond and waterfall as well as the amount of fish, plants, and sunlight. If we keep with the example from above, and you are going to use a skimmer.  You will want a minimum flow of 1,080 to 1,620 Gallons per hour (GPH).

Head

     Head is a measure of resistance to flow.  If a pump has a maximum out put of  20 head feet, it means it can pump water 20' straight up in the air. If a pump is rated at 50 gallons per minute at 10 feet, it means that the pump can overcome 10 feet of head (TDH) and still deliver 50 GPM. As you increase the head, you decrease the flow rate.  To maximize your flow, you must minimize head.  For pond applications the three main sources of head are:

  1.) Static Head - This is the vertical distance you raise the water.  To determine your static head, measure form the surface of the pond (vertically), to the highest point on the discharge line where the water is discharged to the atmosphere.  This is usually the top of your biological filter, or waterfall.  For our example we will say that there is a 4’ rise from the water’s surface to the top of the waterfall.

  2.) Friction Head - As water flows through a pipe and fittings there is resistance. The higher the flow and/or smaller the pipe, the higher the resistance.  Determine your overall pipe length, including equivalent length for your fittings. Consult the friction loss chart. Find where the column for your pipe diameter intersects the row for your flow rate and read your friction loss per 100 feet of pipe.  Use large enough pipe to minimize your friction loss.  It is best to keep friction losses under 6 feet.

  3.) Pressure Head - Any additional pressure required by sand filters, spray nozzles, etc. must be calculated. The conversion is: 1 psi = 2.31 Head Feet

   To determine your TDH, add your static head, friction head, and pressure head.  Now that you know your flow and head, you can select a pump that provides this performance, and does so efficiently. Again, we’ll say that with out 9’ X12’ pond example we have a total of 8’ of head due to plumbing filter and waterfall height. 

Waterfall Flow Rates

     Now we know the flow rate required for our bio-filter, skimmer, and the amount to flow we are going to loose to head loss, there is one more factor we need to add in, the waterfall.  This is where most people fail in their pump selection. You can wing your way through the plumbing and filtration flow rates but when is all said and done, if the flow from the waterfall is wrong, everyone will know and you will disappointed.  So, for attractive, NATURAL looking waterfalls, the industry standard is 1,000 GPH per 1’ or waterfall width. Back to our example, we choose to have a 1 1/2’ wide waterfall on our 9’ X 12’ pond. Therefore we would need a minimum flow of 1,500 GPH to the waterfall. We have included a handy chart to determine the type of flow you would like for your waterfall below.

Waterfall Weir Chart

       Water depth       6” to 11” wide

       Water depth                 12” wide or more

GPH/ per ft. (nominal)

3/16”

1/8”

360

5/16”

1/4”

600

3/8”

5/16”

900

9/16”

7/16”

1680

3/4”

5/8”

2400

1”

3/4”

3300

1-1/4”

1”

4500

Summary

     Now, to put it all together.  We have this 9’ X 12’, 1,600 gallon pond. We are planning on a surface skimmer, a 1-1/2’ wide waterfall that will be 4’ off of the surface of the water.  With the filtration system as well as all of the plumbing, we will have a total head loss of 8’. We need a minimum of 800 GPH to have an effective filter (assuming light fish load).  We also need a minimum of 1,080 to 1,620 GPH to have effective skimming of the pond surface.  And finally, to get that waterfall to cascade like mother nature does, we are going to need a minimum of 1500 GPH flow at the top of the falls.  So we are looking for a pump that has a flow rate of at least 1500 GPH @8’ of head.

   Now you need to decide whether you want to go with a submersible pump, such as an OASE or Tsurumi or an external pump like the Sequence 1000 Series from MDM, Mfg. To illustrate each of these styles we have listed the best pump for this particular pond.

• External:
• Sequence SQK3H - 2,590 GPH @ 4.4’
• Submersible:
• OASE Nautilus 60 - 1,930 GPH @5’
• Laguna PowerJet 7000
• Tsurumi OMU-2