Choosing the Right External
for Your Koi Pond or Water Garden
Now that we’ve (hopefully) convinced you that an external pump IS the way to go - see our article entitled "Singing the Praise of the External Pump" - there’s the decision of which external pump to go with. It’s not an easy decision unless you are like us and do it for a living. There are many external pumps available for water gardens and koi ponds and that makes it most difficult to choose just one. It’s a case of having too many choices – but don’t worry -- we're here to help you narrow down the field.
One pump is rarely the same as another and each has its own set of advantages and disadvantages. Some are designed to give you heavy volume but little head pressure while others will give you great lift. Some must be installed in a flooded suction application while others are designed to be self-priming. It is easy to get the wrong pump unless you know what you are wanting out of it before you begin your search.
Take it step by step. Determine #1 - how many gallons per hour you need going over your waterfall or through your water features, #2 - whether you need a 1 or 2 speed pump, #3 - your electrical requirements, #4 whether the pump needs self-priming capability and #5 - whether you need a low or high head pump. Then choose the model that fits all your criteria.
The smaller the pond the more the water needs to circulate. The rule for ponds up to about 1500 gallons is that you want to turn your water over at least once per hour (or more if you are so inclined). That means you need a filtering rate (rate of water coming out after restrictions and head loss have been factored in) of approximately the number of gallons of your pond. You can turn it over a little less and as slow as once every two hours for larger ponds. The reason for this is because larger volumes of water will hold oxygen levels better and are generally more stable.
Once you know your MINIMUM filtering volume you must address what you want out of your waterfall. 2500 gallons per hour (gph) down a waterfall that is only about 5 feet high and about a foot and a half wide will give you a rather nice waterfall volume. If you increase the width of the waterfall by twice as much you will need 5000 gph to cover it with the same volume of water. The look and sound of the waterfall is subjective to your taste, not ours, but we can give you an idea as to what to expect from different flows.
Remember that the flow we want here is the flow during normal operation while it is filtering. If the pump is a two-speed pump, the normal filtering flow should be the LOW speed. Here’s a few ideas to help you determine how many gph you may want coming over your waterfall:
Fountains need water to run too. A common oversight is to size a pump for the waterfall and not consider any other water feature you may want to add. You’ll need an extra 500 – 1000 gph to run most water fountains. If it’s a simple spitting statue add about 250 gph to the equation. Long streams will require more water flow so factor that in as well.
“Head” is a term used for the height the water is pushed up. If you have a waterfall that is only 2 feet high you can benefit from external pumps rated for “low head” which means that you aren’t lifting the water very high. If you need it to go up 10 feet, however, you cannot use a “low head” pump and get the lift you need out of it while maintaining your desired flow. Sequence is a well-known external pump that has been around for many years. Although it is a very good pump - it lasts a long time and gives you a large amount of flow at low amp consumption - we do not normally recommend it. Sequence is often mistakenly purchased for high waterfalls and simply cannot function in that capacity. We hear from disappointed customers who purchase “low head” pumps such as Sequence and do not understand why their waterfalls aren’t strong or why they aren’t able to push the water up to the top.
Low Head Pumps have big impellers with small motors. They push a lot of water as long as you don't need it to go high. They flow with low energy consumption but the flow will die rapidly with the addition of any resistance. Friction loss, height, distance, elbows in the plumbing, bead filters and other equipment all create resistance.
So when is it good to use a low head pump? Any time you have no need to push the water very high but want the lowest energy consumption possible.
External Pumps for Large Waterfalls
No matter how small or large the pond is if your waterfall is higher than 10 ft. you must plan to purchase a pump that can generate some power. These pumps will generally use more electricity than the low head pumps but you can choose models that are more energy efficient than others. As a rule the more energy efficient the pump the higher the price for the pump but the savings over the years will add up. It makes good "cents" to go the extra dollars and save many times over in the long run.
When selecting a pump for a large waterfall pay close attention to what the manufacturers say about the volume of water at specific head heights. You'll need about 4000 gph for waterfalls of about 2 ft. in width for a nice flow so if the pump is rated 4000 gph at 10 ft. and your waterfall is 10 ft. high the pump will work fine for you. If you want a stronger flow or your waterfall is wider than 2 ft. you'll want one that gives you more gph at that height.
Determining whether you need a 1 or 2-speed pump is based almost solely on if you have a bead filter on your filtering system. Bead filters filter best when the water flows slower through the filter. This allows the beads to trap debris as the water is pushed through the unit. If water flows through most bead filters too fast the debris will simply flow past the beads and back to the pond, making the filter less efficient. Bead filters that do not have blowers attached to aid with breaking up the beads require 4000 to 5000 gph in order to backwash properly. A 2-speed pump is perfect for this situation. The pump would run on LOW for normal filtering operations. LOW is usually very energy efficient. The only time the pump would run on HIGH would be during backwashing or if you just want to show off a rip-roaring waterfall to friends. You would never want to constantly keep the pump on HIGH because it would gobble up electricity like crazy!
This does not mean that you cannot use a high-powered 1-speed pump with a bead filter. If the pump gives you what you want for your waterfall and it runs too fast for proper filtering (over 2500 gph or so) you can plumb it so that with a turn of a valve you can by-pass part of the flow to the filter during normal operation then turn it back so that all the flow goes through during backwash.
Large ponds do not generally benefit from 2-speed pumps. Large ponds with bead filters generally have blowers rendering the backwash speed "high" unnecessary.
External pumps for smaller ponds tend to run off of 115v. Higher powered pumps for large ponds tend to run off of 230v. You might also use a 230 v pump for high volume waterfalls even if the pond is small. When you reach a certain horsepower the manufacturer will only build them in 230v like in the case of the High RPM Artesian pumps by Performance Pro. The top three most powerful models come only in 230v but they are capable of pushing high volumes of water up over 70 ft. Some models will give you an option of ordering them in either voltage while others will be available in only one or the other. Be sure you know which option you are ordering. Also – be sure that the external pump you order has an attached cord and plug unless you are planning to hard-wire it in. In most cases when using 230v codes will dictate hard-wiring.
The term “self-priming” is used to signify pumps that have the ability to pull water a short distance up to fill its priming pot (or leaf basket). This is extremely important! You can only use a self-priming pump if you plan to install the pump on an elevation higher than the level of the pond. Most self-priming pumps will need to be located within a few feet of the side of the pond, otherwise they must work too hard to pull the water up to them and the equipment may fail to operate correctly.
If the pump is located at an elevation lower than the level of the pond, gravity will push the water to the pump and fill the priming pot. The term we use for this kind of set-up is "flooded suction". Flooded suction is the most desirable way to install an external pump but isn’t always feasible. For that reason we have the self-priming pumps. You can use any pump, including self-priming pumps, in a gravity-fed flooded suction application and it’s not critical that the pump be located close to the pond. Just remember, the further the water must go, the more power needed from the pump and the larger in diameter the pipe from the drain to the pump should be.
Although we sell quite a few kinds of pumps, both submersible and external, we have our favorites. These are the pumps we use ourselves and ones that have proven to be everyday work horses. These are the ones we feel comfortable shipping across the country and even out of the country because we know they are good quality and our customers will not be disappointed.
The majority of ponds built are in the 1000-gallon to 2500-gallon size range. For these ponds we have a great external pump that is efficient and effective and reasonably priced. It's called the SuperFlo™. The SuperFlo is a 2-speed pump with an oversized leaf basket. The large leaf basket is perfect for water gardens and koi ponds so it can run longer before the basket needs emptied. The SuperFlo is low head when it is pumping on low speed so if you have a waterfall that is over 10 ft. high, the SuperFlo would not be the one for you. If you have a bead filter and a small waterfall it is probably the PERFECT pump for you.
Here's the information for the SuperFlo External Pump (and yes, you can place an order from this page):
For ponds 2500 to 5000 gallons that do not need lifting power for a high waterfall we have just the pump! It runs off of regular 115v, is very quiet and energy efficient when run on low and is self-priming. It will give you about 3500 gph at 5 ft. It's Performance Pro's Artesian 2-speed Model #A2-3/4. Click HERE to see it.
Low-Head 1-speed Pumps:
You do not necessarily need a 2-speed pump like the SuperFlo unless you have a bead filter. Performance Pro has several high-volume, low-head, energy efficient pumps that will work fine for ponds of almost any size as long as you don't have a high waterfall. We prefer the Performance Pro Artesian Low RPM models for low head applications because these run very quietly and are extremely energy efficient. We like dealing with Performance Pro because their customer service is outstanding and their products are of the highest quality.
If you have a waterfall that is high and need a pump with some power we invite you to check out Performance Pro's Artesian High RPM external pumps. We use several of these ourselves and the Doc is absolutely delighted with them. He swears by them because they move a lot of water with minimal amount of motor noise.
Click HERE to go to the Performance Pro page of our online store.
I hope this article was helpful. It isn't always easy to choose the right pump for your system. Unfortunately once a pump is used it can't be returned so picking the right pump from the start is very important. One of the best things about purchasing through PondDoc.com is that you do get the benefit from our experience so if you need Pond Doc to help you choose the right pump please feel free to call him at (770) 663-6325 or email him.
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