The pond pump is the life blood of any koi pond or koi watergarden. Whether building a new pond or replacing an existing pump, there are many choices when it comes to buying a pump. There are also many things to consider when choosing the type and size of pump to purchase. Most koi ponds have a skimmer for handling mechanical and some biological filtration. This is where the main pump is usually located and provides most if not all the water movement for the entire pond. The pond can have more than one skimmer or the skimmer may have more than one pump depending on the size and shape of the pond. There can be a stream or water fall or a combination. An external filter or protein skimmer may also be involved.
The first thing to consider is how much water flow is needed for the koi pond or koi watergarden. Ideally the entire volume of the pond water needs to be turned over once every two hours. For example a 5,000 gallon pond would require 2,500 gallons per hour flow rate. To calculate the volume of water multiply the average length times the average width times the average depth to get the cubic feet of water. Multiply the cubic feet times 7.5 to get the volume in gallons. For example a pond 12 feet long, 8 feet wide and 2.5 feet deep would have 240 cubic feet of water (12 x 8 x 2.5 = 240). 240 x 7.5 = 1,800 gallons of water. This would require at least 900 gallons per hour of water movement. The next thing to consider is how high the water has to be pumped. This is called head pressure, which most high quality pumps will list in their specifications. For instance, a 1,200 gph pump may only pump 900 gph at 3 ft. of head pressure. The size of pipe will also make a difference in the pump flow rate. For best flow rates the pipe inside diameter should be 1/2 inch larger than the pump outlet size. If a pump has 1 1/2 inch outlet the pipe inside diameter should be 2 inches for best flow rates. The piping will still cause some restriction and 100 gph for every 10 feet of piping should be added to the pump size. Now lets put it all together. The pond is 12 x 8 x 2.5 and has a waterfall that is 3 feet above the water line and the total length of pipe used is 20 feet. 12 'x 8' x 2.5 '= 240 cubic feet. 240 x 7.5 = 1,800 gallons. 1,800 / 2 = 900 gph. 900 + 200 = 1,100. The pump size needs to be at least 1,100 gph @ 3 'head pressure.
Types of Pond Pumps
There are 2 main types of pond pumps. The most common type is the submersible pump which is usually submerged in the pond skimmer. There are also 2 types of submersible pumps. The first type is the magnetic drive pump, producing lower flow rates and maximum head pressure than other types of pumps. It typically uses less electricity and is very cost efficient to run. The most popular magnetic drive pump is the Pondmaster Mag Pump. These pumps range in sizes of 200 – 2400 gph. The drawbacks are that they do not pass solids of any size and must be used with a pre filter. They are great for running small fountains, UV sterilizers, and small waterfalls. The next type of submersible pump is the direct drive pump. They have more power than the magnetic drive pumps and much higher flow rates. They also are able to pass solids up to 10 mm in diameter. This type of pump uses more electricity than the magnetic drive pumps. ShinMaywa pumps are rated the most durable and cost efficient direct drive submersible pumps on the market. These pumps range is sizes of 3,300 – 31,800 gph with maximum head pressure of 49 feet. The Pondmaster Hy-Drive utilizes both technologies of magnetic drive and direct drive pumps. Hy-Drive pumps are very cost efficient to run and range in sizes of 1,600 – 6,000 gph. They do not pass solids as well as the direct drive pumps which is not a factor if used in a skimmer that has a mechanical filter. They are great for medium size koi ponds or koi watergardens. The Pondmaster Hy-Drive 4800, rated at 250 watts with a max head pressure of 18.5 feet is the most cost efficient pump on the market.
The second type of pond pump is the external pump. They are mounted outside the water and can not be submerged. The benefits if this type of pump are higher flow rates, durability, and cost efficiency. External pumps are typically used in larger pond applications, and last twice as long as a submersible pump at half the cost of electricity. The market leader in external pond pumps is Sequence Pumps. Sequence pumps range in sizes from 3,300 – 7,800 gph with a maximum head pressure of 24 feet.
Cost of Ownership
Cost of ownership has to be considered when purchasing a pump. A koi pond or koi watergarden pump has to run 24 hours a day and in many zones 365 days a year. The cost of ownership is the price of the pump, how long it is expected to last, and how much it cost to run. There are many types and brands of pumps on the market with a wide array of prices. The cost of the pump is only one factor. A cheaper pump that has to be replaced every year and burns twice the electricity is not a good value. The warranty period and wattage rating of the pump must be compared along with the price of the pump. The lower the wattage, the cheaper the cost to run the pump. The longer the warranty period means the longer the pump is expected to last. Keeping the pump and pre filter clean makes the pump more efficient and last longer.