Just like your body has a heart to circulate healthy blood through your system, your pond has a pump to circulate the water over the falls, providing beneficial aeration for your pond critters and plants. Choosing the right pump is essential for ensuring that you create an adequate flow of water for your waterfall or stream, which in turn maintains water quality that’s fit for your pond ecosystem.
Several pumps are on today’s market, from sump pumps and swimming pool pumps to pumps made specifically for water gardens with magnetic drives and fish safe oil-less designs. So how do you choose? What are the most important features?
How much water flow?
There are a few different ways to decide how much water flow you need.
Flow over the waterfall: It’s common for first time pond builders to underestimate just how much water they want flowing over their waterfall. For example, 1,000 GPH (gallons per hour) sounds like a lot, but if you break it down, that’s only about a quarter gallon per second. Then if you take that quarter gallon and spread it over a 2 foot wide waterfall, you’re probably going to be disappointed with the trickle you end up with. Also, the sound of a waterfall usually becomes one of a pond owners favorite parts of their water garden. So, one of the first things you should consider is how much water do you want flowing over your waterfall and how wide will that waterfall be?
- 50 GPH per inch = This is trickle/dribble territory (~1/4 inch deep).
- 100 GPH per inch = Now you have a solid sheet of water flowing over the clean edges. You’ll get some soothing sounds with this much flow (~1/2 inch deep).
- 200 GPH per inch = A solid, strong, more dramatic flow of water that creates enough sound to be heard 30 feet away (~1 inch deep).
Water Quality (no fish): The generally accepted rule of thumb here is that you want all the water in your pond to circulate at least once every 2 hours. So if you have a 1,500 gallon pond, you will want at least 750 GPH of flow.
Water Quality (with fish): If you have fish in your pond, you want more filtration. For most pond setups, the main pump drives water through the filtration system; so more flow equals more filtration. A safe bet is to double the flow if you have fish – so for a 1,500 gallon pond, you will want 1,500 GPH of water flowing. Having extra flow will help your pond support more fish, but you want to be careful not to exceed what your pond can handle. The average pond can support 1″ of fish for every square foot of pond surface area (e.g. a 10′ by 10′ pond has 100 square feet of surface area, so you could support 20 5″ fish or 10 10″ fish or 10 5″ fish and 5 10″ fish, etc.). Another way to calculate this is 1″ of fish for every 10 gallons of water in your pond. You want to err on the conservative side here – fewer fish are happier fish. Don’t forget to allow for growth (and breeding!). Predators will “help” here…
What size pump?
So once you know the amount of flow you want, it’s time to figure out how big of a pump you need. Pump performance (i.e. the actual amount of water flow you will get out of your pump) will vary depending on how much resistance it’s pushing. A term to become familiar with is “total dynamic head” (TDH), which refers to the pressure on a pump caused by the interactions of flow rate, pipe diameter, pipe length, elevation, and pipe material. The more resistance that a pump encounters, the stronger pump you’re going to need. In other words, a 3,000 GPH pump only maxes out at 3,000 GPH. The more resistance you throw at it, the less actual flow you get.
Here’s a chart that shows how head pressure effects the Aquascape AquaSurge pumps (this is pretty typical):
And a similar chart for Atlantic Water Gardens Tidle Wave pumps:
As you can see, the amount of head pressure you have on your pump has a significant impact on the actual amount of water flow your pump will produce. With 15′ of head, a lot of pumps are producing half their maximum rated flow. So the next question we need to answer is how much head pressure will my pond produce? This requires a little simple math. You’ll need to add up the following:
- Add 1 foot of head pressure for every foot of vertical lift (from the surface of the water to the top of the waterfall)
- Add 1 foot of head pressure for every 10 feet of hose or pipe
- Add 2 feet of head pressure for every 90 degree fitting
- Add 1 foot of head pressure for every other type of fitting
#1+#2+#3+#4 = the total feet of head pressure
So for example, if you have a pond with a 5 foot waterfall, 20 feet of pipe, 1 90 degree fitting, and 1 other type of fitting, you would add it up like this:
5 (from the vertical lift) + 2 (from the feet of pipe)+ 2 (from the 90 degree fitting) + 1 (from the other fitting) = 10 total feet of head pressure
So you take the pumps performance chart, the amount of flow you want and the calculated head pressure of your pond and use those numbers to determine what size pump you need.
Cost to operate
One more calculation you want to be sure you run is the cost to run the pump. Your pump will run most of the year (and for many climates, all year), so the electricity costs shouldn’t be ignored (especially if you’re still in the planning phase).
Most pumps have a watts rating. This tells you how much power the pump draws. You want to take that and multiply it by how much time the pump runs and multiply again by the cost of electricity (usually in kilowatt hours). We can transform the pump wattage to kilowatts by dividing by 1000. If we want to figure out the cost per month, we’ll need that number in hours, too (so we take the average number of days per month [30.42] and multiply it by the number of hours in a day  to get 730.08 average hours in a month). So the formula to figure out the monthly cost to operate the pump looks like this:
(Pump Wattage/1000) X (730.08) X (your electricity cost per KWH) = Cost to operate your pump per month
So to do an example, let’s say you are using the 4000 GPH AquaSurge pump (220 watts from the chart above) and you pay is $0.0983 per KWH (this was the US average in 2009).
220/1000 X 730.08 X $0.0983 = $15.79 per month
Since your pump will be running non-stop for most (if not all) of the year, the reliability of the pump should be a major part of your decision. When your pump dies, your pond starts suffocating.
Once you’ve narrowed it down to a few brands of pump, look online for reviews. You want to find unbiased evaluations of these brands to see what other pond owners have experienced. If you know other pond keepers, it’s always good to ask them, too.
How long of a warranty does the pump come with? This can be a good clue to how reliable the pump is.
This is also a major reason you want to buy a pump that is designed specifically to work in a pond. It might be tempting to substitute something like a sump pump here (on paper they look comparable, good GPH, etc.), but that decision will likely turn into a major headache later. Sump pumps aren’t designed to be run 24 hours a day, and it won’t be long before it burns out.
Pipes and Plumbing
In addition to your pump selection, you’ll want to give careful consideration to plumbing needs. An incorrect choice of pipe can cause friction and reduce the amount of flow your pump can produce. Above 4,800 GPH of flow, you want to move up from 1.5″ diameter pipe to 2″ pipe. Otherwise, the pipe itself will throttle your water flow.
They type of pipe is also important. Flexible PVC pipe is a popular choice for pond projects since it can handle the turns and tight corners that often accompany residential installations. Not only that, but flexible PVC pipe contracts and expands with seasonal changes, eliminating potential plumbing headaches.
Enjoying the Results
When purchasing your pond’s pump, you can always consult with the retailer’s water garden expert to ensure you’re making the proper selection (Great idea! Let them do the math : ). With the correct pump in hand, you’ll enjoy the delight of every pond owner when they first flip the switch and watch the cascade of water flow over the falls and into the pond (or you’ll frown and scowl at the wimpy trickle). All that’s left after adding the final touches of fish and plants is to pull up a chair, kick up your feet, grab a drink and enjoy the sight and sound of your beautiful waterfall and pond.
So what pump are you using? I’d love to hear about your experiences in the comments. Thanks!!