What size pond pump do I need?

What size pond pump do I need? | Warehouse Aquatics | Middlewich

If you’re building a garden pond, choosing the right-sized pond pump is essential to your pond health. Choosing the wrong pump can lead to all sorts of problems and prevent fish from living in the water.

Not to worry, though. In this blog post, we’ll tell you everything you need to know to choose the right-sized pump.

Why do I need a pond pump? | Warehouse Aquatics | Middlewich

Why do I need a pond pump?

Most ponds need a pump to circulate the water. The only exception to this is naturally occurring wildlife ponds that have a natural stream of water flowing into them.

If you’re adding fish to your pond, a pump is essential to keep your water clean and safe for your pond inhabitants.

You can choose between submersible pond pumps, which sit at the bottom of the bond, and external pumps, which sit above the water line or outside of the pond.

How do I measure the water in my pond?

There are a few things to consider before you choose a pump. First, you need to measure the volume of water in your pond. You can use this Blagdon calculator to work out how much water there is in your pond.

How do I measure the water in my pond? | Warehouse Aquatics | Middlewich
How do I measure the head of water? | Warehouse Aquatics | Middlewich

How do I measure the head of water?

Once you’ve calculated the volume of water in your pond, you’ll need to do a second calculation. This one is to do with the head of water that your pump will need to handle. The head of water is the height of water at its highest point from the pump to the top of a waterfall, a stream, or your filter system. 

To calculate the head of water, measure the height of the water from the pond pump to its highest point. So, if the highest point is a waterfall that stands 120 cm above the pump, the head would be 120 cm. As you don’t have a pump yet, measure from where the pump will sit.

How do I measure piping to calculate the head of water?

If you have a waterfall, stream, or filter system in your pond, you also need to know the length of pipe that the pump must move water through to get to the top of this feature. 

For example, if you need 300 cm of pipe to reach the top of a waterfall in your pond, this will affect your head calculation.

For every 300 cm of pipe, you need to add 30 cm to your head calculation. So, if you had 120 cm of height and 300 cm of pipe, you would have a head of 150 cm.

As the pond pump pushes water upwards towards the head height, the pump’s flow rate may decrease. Therefore, if you don’t take head height into consideration, the pump that you think is the right size may be underpowered for the volume of water you need to circulate.

All pumps have a maximum flow rate, which is rated at a zero head height. This is because as you increase head height, the flow rate decreases, sometimes to half the original flow rate. 

Most pumps have a flow chart that shows the flow at different levels of head height, which you can use to choose your pump.

All pumps also have a maximum head height, which refers to the height of water the pump can handle. Once the water reaches this level, the flow of water will slow and then stop.

How do I measure piping to calculate the head of water? | Warehouse Aquatics | Middlewich
How do I measure circulation per hour? | Warehouse Aquatics | Middlewich

How do I measure circulation per hour?

For your third calculation, you’ll need to work out your circulation per hour. This measurement refers to the volume of water that your pump can circulate in an hour. So, a pump that matches the volume of water in your pond (including the head) should circulate all the water in your pond every hour. 

There are various schools of thought on how often you should circulate your pond water. Some people say once an hour. Others say once every half hour. We suggest that you measure the size of your pond to work out how often you need to circulate the water. More on that below.

You should also take the stock of your pond (fish and plants) into consideration here. If you have a higher-stocked pond, you might opt to circulate your water more frequently.

Pond pumps for small ponds

Much like bigger fish tanks are easier to maintain than smaller fish tanks, larger ponds are easier to maintain than small ponds. This is because of dilution. The smaller the volume of water in a pond, the more toxins from fish waste and debris build up. A small pond will struggle to dilute the waste in the limited volume of water available.

So, if your pond holds fewer than 4,500 litres, we suggest you circulate your water every half an hour. To do this, you’ll need a pond pump with a flow rate that can handle double the size of the volume of water, plus head.

For example, if you need a pump that can circulate 3,400 litres of water once an hour, you can double the size of the pump to 6,800 litres to circulate the water twice an hour.

Pond pumps for small ponds | Warehouse Aquatics | Middlewich
Pond pumps for medium ponds | Warehouse Aquatics | Middlewich

Pond pumps for medium ponds

Typically, a medium pond of 4,500 to 9,000 litres needs to circulate its water once an hour. You can get away with circulating a medium-sized pond less frequently than a small pond because there is enough water to better dilute waste in the pond.

So, for example, if your pond needs a pump that can circulate 6,800 litres an hour, you can go ahead and buy this pump.

Pond pumps for large ponds

As there is so much more water in a large pond, it’s much easier to dilute waste in these than it is in smaller ponds. Therefore, if your pond holds more than 9,000 litres of water, you may only need to circulate it every two hours. 

In this case, if you calculate that you need a pond pump of 13,600 litres, you can half this and buy a pump that can only handle 6,800.

So, you might find that you end up using the same-sized pump for your small or medium pond as a fishkeeper who has a large pond. 

Finley the Fish | Warehouse Aquatics

Bonus Tip

If you haven’t yet built your pond, keep in mind that a large pond can be just as cheap and easier to manage than a small pond. 

That said, you will need to invest in a pond filter that can handle the volume of water that the pump sends through. Your filtration system needs to match the pump’s flow rate.

Lots of filter systems also come with a UV clarifier, which destroys single-cell algae that turns pond water green. However, if you buy a separate UV clarifier, make sure you buy one that matches the pump’s flow rate. 

Pond pumps for large ponds | Warehouse Aquatics | Middlewich
Accommodating waterfalls | Warehouse Aquatics | Middlewich

Accommodating waterfalls

If you have a waterfall, the amount of flow from your pump dictates how much water cascades down your waterfall. If you want to increase the volume of water that cascades down your waterfall, you can add an additional pump alongside your filter pump. 

Alternatively, you can run one pump for your filter system and another for your waterfall. This way, you can turn your waterfall pump off when you don’t need it, leaving only the main filter pump running to maintain water quality. 

Choosing a pond pump

When you’ve measured the volume of water in your pond, the head of water, and the number of times you need to circulate your water per hour, you can choose a pond pump that meets your needs.

The charts that come with most pumps should help you decide which is most suitable. If in doubt, opt for the larger pump. 

Remember that you can never have too much filtration (but you can have too little), and you’ll rely on your pump to supply the water to the filtration system.

Choosing a pond pump | Warehouse Aquatics | Middlewich

About Warehouse Aquatics

The Warehouse Aquatics mission is to offer the most choice at the best prices when it comes to your fishes’ wellbeing. We use the products on our website ourselves and are well-versed in all things fish, so we can give you all the advice you need. We’re not just here to sell aquatic supplies. We’re also here to guide you through your journey as a fish owner and enthusiast.

As a small team, we love to hear from our customers, so please do join the Warehouse Aquatics social media community. We’re always up for a chat, and we’d love to share your aquarium photos with our followers.

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