What Size Pump Do I Need

It is generally accepted that Koi ponds should turn over all the water in the pond each hour. That would mean that a pond with 1000 gallons of water should be using at a pump that produces at a minimum of 1000 gph. Keep in mind that other factors such as head height, friction loss and pond filtration can reduce the flow sometimes up to 40%.

Another factor to consider when choosing your pump is if you have a waterfall you may need an even larger pump depending on the visual effect you want to achieve. The rule of thumb for waterfalls is that for a normal flow you will need approximately 100 gph for each inch of width of the initial waterfall. In the example above if your 1000 gallon pond has a 12” wide waterfall then you would need 1200 gph at the top of the first spillway ( 100 gph X 12 = 1200 gph) If however, you wanted a stronger flow such as sheeting or more noise you would need a minimum of 200 gph for each inch of width or 2400 gph using the example above. The flip side of this is if you wanted only a zen like trickle it could be as low as 50 gph per inch. In most cases you can reduce the water flow from your pump if it is to strong using a ball valve but there is nothing you can do if it is not strong enough. For this reason it is best to purchase a larger pump if you are in doubt.