The right selection for your new or existing water garden

Pumps for Ponds, Water features and Waterfalls

Calculating the size of a pond pump depends upon the size of your pond and also whether you are using the pump for filtration, a waterfall or just re-circulating water.  The number of fish your pond contains will also influence your decision, as larger fish populations have greater oxygen requirements.   A good rule of thumb is that a pump should be able to pump out about half the pond volume every hour. So a pump that moves 500 gallons per hour would be appropriate for a 1,000 gallon pond.  To determine the size pump you’ll need, first calculate the volume of your pond.

• Pond volume (gallons) = 7.5 x average width (ft.) x average length (ft.) x average depth (ft.)

If you are using the pump for filtration only the calculation is simple.

• Flow rate for filtration- Filtration flow rate in gallons per hour (gph) = 0.5 x pond volume (gallons)

If you have decided to also power a waterfall or water feature with you pond pump you will want to decide what that water feature requires to obtain the look you want to achieve. (Note, if your sizing for a waterfall or water feature and this is greater than the requirement for it is for filtration make sure to check your filter ratings as you may need to upsize the filter to handle the extra flow.)

Flow rate for fountains/water features

• For every inch of water spillway width at the top of the fountain, you need 100 gph at the height you’re pumping

Flow rate for waterfalls

• Light flow = 50 gph x waterfall width (in.) – This is about the same as one garden hose.
• Average flow = 100 gph x waterfall width (in.) – This is about the same as two garden hoses.
• Strong flow = 200 gph x waterfalls width (in.) – This is about the same as four garden hoses.

Finally once you have established the flow rate or volume you are trying to get you will then need to calculate the height to which your pump needs to push that water and compare it to the pump flow chart to make your selection.

Head height calculation

• Total length of pipe (ft) / 10 + vertical lift (ft) above water level = head height (ft)

Designed to be wholly submersed in water, in the deepest part of the pond.

• Easy to install
• No need to camouflage the pump
• Run very quietly so they are not distracting in your garden
• Submersible pumps can be used to drain your pond, if needed
• Locate either directly into your pond or in a skimmer box or pond vault
• Flow rates from 50 to 12,000 gallons per hour
• Some types consume more energy and increase running costs than other types
• For smaller ponds, submersible pumps are generally most economical

Tip: Some submersible pumps use oil in their operation, there is the danger of the pump seal failing and leaking oil into the water.  If you have fish or other aquatic life in your pond, you’ll want to look for a submersible model that uses a safe grade of oil.  Do not use a pump designed for other uses for this reason.

External pumps can move a high volume of water and still manage to outperform submersible pumps in energy costs. Although a little more technical to install, external pumps are generally more reliable.

• Available as self-priming pumps able to draw their own water
• Pumps that are not self-priming can burn out a motor if the power shuts off momentarily and then returns, so protect against this by installing a check valve
• Low quality ones can be loud, disturbing the quiet of your garden
• Work well for larger ponds — 1,000 gallons and above
• Offer long-lasting performance and easy repair
• Install external pumps in a dry location
• Require less routine maintenance than submersible pumps