Choosing a Pond Pump

Choosing the Best Pump for your Koi Pond

The pump is the heart of the pond.  It keeps everything moving and flowing.  No koi could survive in any pond without a pump circulating and aerating the water.  Some water gardens can survive without a pump but they have lots of plants and only one of two goldfish to control bugs.  Koi ponds, or any pond with fish, need a pump.  But of course you may have many questions like what type do you need?  Submersible?  External?  What's the difference?  And how big?  What is "head pressure"?  How do I know if it will last?  And what will it do to my electrical bill?  So many questions and so many choices.  Lets take a moment here and try to sort it all out.

First we need to decide the size of the koi pond.  As a general rule you want to circulate to entire volume of the koi pond through the filter once per hour as a minimum.  So a 2000 gallon koi pond needs at least a 2000 Gallon Per Hour (GPH) pump.  You can go bigger if you like, but it's usually best not to go smaller.  Also, consider other aspects of the koi pond, like the size of the filter and the UV.  These are best chosen after you decide on the pump to make sure everything is the right size for the flow rate.

Ok, so you have decided on the size of the koi pond and you know the GPH you want for your pump, right?  But wait, what about head pressure?  Ah, yes factoring in head pressure is an important consideration.  Head pressure is basically the height you want to pump the water.  The higher you go, the greater the head and the less water the pump will move.  Most pond pumps are designed for low head, this makes them far more energy efficient, but you need to factor in how much head the pump can handle and make sure you have the right GPH after head.  If the pump is at pond level and the waterfall is 5 feet higher then the pond, then that's 5 feet of head.  But other things can increase head pressure as well.  Turns or angles in the pipe, pressurized filters and reducing the pipe size all contribute to head pressure.  So keep all this in mind before you buy.  Also, keep in mind, pond pumps push water far better then they pull water.  So placing the pump close to water level or even lower then water level will greatly increase its flow.

Ok, so now you have factored in your head pressure and you know what size of pump to get.  So now its time to decide on the type.  There are two main types of pumps.  Submersible and external.  Submersible pumps are much easier to install and generally cost less to purchase.  They are also available in very low GPH that you can't find in an external pump.  This makes them a good choice for smaller ponds and DIY pond builders.  However they also require more frequent cleaning and they tend to use a bit more watts when compared to external pumps.  Now external pumps do require more plumbing and they can cost more to purchase, but for most ponds they are a better choice because of their lower maintenance and lower operating costs. 

For very large koi ponds with high head, you may be tempted to get a large pool pump.  These are very high head pumps that use tons of electricity.  But some installers use high head sand filters instead of a koi pond filter and install these monster pool pumps in order to get the water through these filters.  Almost always the cost of replacing these giant pumps with a low watt, low head pond pump pays for itself very quickly.  You may need to find a way to reduce the head pressure so this will work.  For example, if you are using a sand filter, replacing the sand media with plastic koi pond style media will greatly reduce the head pressure created by the filter which will allow you to use the lower head pump.

The next thing to consider is the placement of the pump in the koi pond. If you are using a submersible filter, it's best to place it in the deepest part of the pond.  Many times the submersible pump will be placed in the skimmer to prevent clogging, however if this is the only form of circulation for the pond, the pump will not be able to remove the majority of the waste from the skimmer box.  The fish waste will sink to the bottom and remain there.  But if the pump is placed at the bottom, then the fish waste can be removed by the pump and sent to the filter.  However this creates a new problem, the pump will clog frequently and need to be pulled up and cleaned to prevent it from running dry and burning out the bearings.   A good pre-filter is needed in this situation.  The best placement for a submersible pump is in a settling chamber.  A settling chamber has the dirtiest water flow from the bottom of the pond to the separate drum or tank via gravity.  The heavy solids settle at the bottom of the tank and the pump pulls the clean water from the top of the tank.  For more information on settling chambers and their use in a koi pond, please read this article.

The problems listed above are why many people will choose an external pump.  This sits outside the koi pond and pulls water from the pond.  Preferably it will pull water from the bottom of the koi pond either directly from a bottom drain or through a settling chamber.  If you have a skimmer, the external pump can pull water from both the skimmer and the bottom drain.  It's this flexibility that makes external pumps the best option for most ponds. 

One thing to keep in mind about external pumps.  If they sit above water level the pipe going from the koi pond into the pump needs to remain primed when the pump is turned off.  Otherwise, when you turn it on it will run dry.  That's one problem you don't have with submersible pumps.  Some external pumps are self priming, or you can add a priming pot in front of the pump.  The priming pot is a good idea because it is also a leaf trap that will protect the pump.  You will also want to install a check valve in the line before the pump and below water level.  The check valve will allow water to flow only one direction into the pump, as soon as the water flow stops then the water in the pipe remains there.  The best type of check valves for pond pumps are "swing" check valves.  These have less resistance then "spring" valves.  Spring valves require pressure to pull them open and pond pumps don't pull very well.  So always use a swing check valve before the pump.  You can also dig a pit and install the pump below water level.  This will remove any concerns about priming and increase the efficiency of the pump since it doesn't have to pull any water.  However you need to make sure the pit cannot ever fill with water as the pump will flood then short out and need to be replaced.  Also, instead of a check valve you will want to install a ball or gate valve between the koi pond and the pump.  This way you can stop flow from the koi pond to the pump during maintenance.            

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