How To Specify Your Pond Pump ... Flow Rate and Maximum Flow

Every pump behaves differently and most submersible pumps operate between what is called maximum head (a point at which pump flow stops) and maximum pump flow which is the flow the pump can develop without any pipe attached (in other words that flow that could be achieved at the pond surface level only ... in other words no head.

In practical garden fish pond situations more often than not the pond pump flow refers to the amount of water required to give you the waterfall effect. Calculating this flow is possible or you can do a simple waterfall flow test  you desire. Guessing is no good here.

You need to know the correct pond pump flow and pump head for your application. If your pond pumps does not deliver enough water flow then your waterfall will be an disappointment. If you create too much flow this can be just a waste of your money (in electrical power use). In addition it can create a noisy rather than soothing waterfall flow that will annoy you and your neighbors. 

When choosing the correct hose for your garden pond, you'll want to select a ribbed hose that not restrict pump flow, especially around bends and curves that are usually required in a pond waterfall application. 

When you're shopping for a pump, you will normally see a maximum pump flow rating on the outside of the pump box. You need to treat any information on the outside of a pump box with some caution. Maximum pump flow is the amount the pump can supply WITH NO HOSE ATTACHED TO IT. This is an impractical measurement unless you just want to circulate water within the fish pond (ie the pump has no pipe attached).

Determining your pump flow rate

A pond pump's flow is the amount of water that will be pumped through your pond system to get the waterfall effect you're looking for. The pump flow must also take into consideration your biofiltration system. If you're operating a pond with a biofilter and UVC and no waterfall aim for turning the pond volume over every 1 to 2 hours ... this means go for a flow rate between that of half the pond's volume and the full pond volume per hour.

For example, if your pond has a volume of 2,000 gallons, then you'll want to choose a pump that will circulate between 1000 and 2000 gallons per hour. It's usually better to chose a pond pump that's one size larger than you think you might need if you're not completely sure of the pump volume you need. Remember in practice the pump has to overcome pressure drop through fittings and bends and the pipe itself so getting a slightly bigger pump than theoretically needed is always a good idea.

If you are running a waterfall in your garden pond, you'll need to determine the pump head before selecting a pump. As a quick summary, pond pump head is the height (measured from the SURFACE of the water) to the inlet of the waterfall. In other words, this is the height to which the water must be lifted in order to operate the waterfall.

A good idea when operating a waterfall in your garden pond is to run two separate pumps. This will have the added benefit of saving you money in electrical consumption.

You'll always see pump head and flow information on the manufacturer's product box.

Free pump calculators here