Choosing a pump takes a little work, you can’t just run out and get any old pump that’s on sale and hope it works. You need one that’s going to be able to run the pond you’re building and that could be as small as a 100 gallon preformed pond to 10,000 gallon show pond full of prize wining Koi. So hear are some things to think about and how to figure them out.
- How many gallons is the pond?
- Do you have a waterfall and if so how high and wide is it?
- Is the pump going to have to more the water a long way before returning to the pond?
- Will you have a long twisting stream that starts on the other side of the yard?
- What style of pump are you going with, in the water or out of the water?
- Are you going to be ok with just one pump or will you need two?
- Fish load
- Voltage / Energy Consumption
Calculate Your Pond Water Volume
For Rectangular Pond: Water Volume = length (feet) X width X average depth X 7.43 gallons/cu. foot = GALLONS
For an Oval Pond: Water Volume = 0.8 X ( length (feet) X width X average depth X 7.43 gallons/cu. foot) = GALLONS
It is recommended that pond water is circulated at least once per hour. For example, if you have a 500-gallon pond, you need a pump that runs 500 gallons per hour at the height of the discharge.
Head equals the total number of feet from the top of the waterfall to the water’s surface. For example: Let’s say that height is equal to 5′. In general, you will need 1,500 gallons per hour (gph) for every 1-foot of waterfall discharge for an average flow.
Measure the diameter of the fountain spout with a tape measure. You will be calculating the gallons per hour, or GPH, by multiplying the diameter by 100. For example, if your fountain spout is 1 inch in diameter: 1 x 100 = 100 GPH, your pump will need to be rated at 100 GPH.
Fish Load (How many and how big)
There is no true number on how to figure this value out but pond fish generally need 10 gallons of water for every inch of their length. The more fish you have, the more filtration and circulation the pond will require. It is recommended to keep the fish load below the what you estimate to be the maximum capacity of the pond. If you are running a Koi pond, the more flow and circulation is required than a pond that is filled with plants and handful of goldfish.
Approximation of adult size fish:
- Koi = 30″
- Comet Goldfish = 14″
- Shubunkin Goldfish = 12″
Most pumps designed for ponds are wired for 110V, which can be plugged into any GFCI (Ground Fault Circuit Interrupter) outlet in the USA. When assessing the energy consumption of a pump the lowest wattage possible is recommendable. Each additional watt helps to build on the electric bill, which may be surprising when a pump is running 24/7. Generally, external pumps use less energy than submersible pumps when you get to the 3000 – 4000 GPH range and up.
In addition, most external pumps last much longer than submersibles. A good 6000 GPH external pump should be capable of running properly using no more than 450 watts, where as a standard submersible pump can use anywhere in the range of 750 – 1200 watt. Just remember when making a selection to consider energy consumption. Just remember that can a low watt pump can easily save hundreds of dollars over the year on your electric bill.