Choosing The Best Pump For Your Pond
Just as there are many different sizes, shapes and styles of ponds in our gardens, there are also just as many different types, sizes and capacities of pond pumps. So what one is right for your pond? This article helps you to make an informed choice.
First you must decide on whether you want a submersible pump or an above ground pump. Each has its own pros and cons. An above water pump is of course easier to maintain. It is also less likely to become damaged by water borne particles such as sand or gravel. Being above ground they can be housed so as not to be seen and are not taking up any space within your pond. They can however be a bit noisier and are usually a little more expensive. A submersible pump is the most popular choice for smaller ponds as it is silent in operation and can be lowered out of sight into the pond. Of course it does have to be removed for cleaning and maintenance.
Secondly you need to ask yourself why you need a pump. Is it for filtration, a waterfall, a spouting water ornament, a stream or fountain? Each of these features will have differing needs so let’s take each in turn.
Pond Pumps for Filtration
Firstly you will need to know the volume of water in your pond in litres. This can be calculated approximately by multiplying the average length by the average width by the average depth in feet and multiplying these figures together.
Then multiply the answer by 6.25 to get gallons. Multiply again by 4.25 to get the answer in litres.
So for example if your pond is 8 feet by 5 feet at 3 feet deep then
- 8 x 5 x 3 = 120 cu ft
- 120 x 6.25 = 750 gallons
- 750 x 4.25 = 3187.5 litres
For best results, you need to turn over the water every hour and a half to two hours in a normal goldfish pond or every hour for a koi pond. You now know how many litres you have in your pond and as pumps are rated in the UK by the number of litres per hour they can turn over, you know what size of pump to buy. In our example above, a pump of at least 1600 litres an hour for a goldfish pond, or 3200 litres an hour for a koi pond.
However, you will need to increase this slightly depending on the distance over which you are pumping your water. This is because some flow rate is lost due to friction in the pipework. The height to which you are pumping will also have an effect on this. If you are unsure, remember you can always reduce flow but you can’t increase it so it is best to go for a larger size.
Pumps for Waterfalls and Fountains
In order to supply a water feature above the height of the water surface then you will need additional pressure. As soon as you start pumping water uphill, flow rates decrease dramatically. You will need to look at the head rate or head height rating of the pump. This will dictate the vertical distance between the pond water surface and the highest point to which you are pumping.
Just remember that the higher you pump the water, the slower the flow rate will be. Most hood quality pumps will state the head rate. Also bear in mind that if your system contains a filter and UV, then you will need to allow about 2ft of additional lift to compensate for the additional pressure required.
For waterfalls, you will also need to factor in the width of the spill back into the pond. A waterfall generally needs at least 250ltr/hr. for every inch of waterfall lip width. Therefore assuming a 10″ waterfall lip, that gives us 10 x 250 = 2500ltr/hr. This is in addition to the calculation already done to circulate the water every hour or two. So for a pond of 1800ltrs, the minimum pump size needed to turn over the pond water every 1 to 2 hours and run the waterfall would be 2500 + 1800 = 4300ltr/hr.
The above figures do not take into account plumbing which will also slow down water flow, therefore the pump may well need to be even bigger.
So in summary, when buying a pump you should know the water flow of the pump at the maximum height of your pipework and outlets to your pond. The higher you want to raise the water the less water will be pumped.
Always remember, you can use a valve to adjust the flow of a pond pump but you can’t increase the pumps capacity.
The only other consideration is the cost of electricity. An elaborate system looks great but if you can’t afford to run it, it will become a stagnant pain in the wallet. Think within your budget.
A Word On Pond Pump Safety
Remember when deciding on your pump to allow for getting an electricity supply to it. It must be fitted with an RCD to eliminate any danger of electric shock. Always use waterproof connectors. For details you can visit our page on waterproof pond connectors. Wiring should be armoured if exposed or over long distances and in a conduit at least. If you don’t know what you are doing, seek professional advice.
Tie string to the handle of submersible pumps and tie the other end to a tent peg. Fix the peg into the ground at the side of pond. Now you can easily pull up your pump for maintenance. Don’t ever pull a submersible up by the power cord.