Pond pumps – A comprehensive guide

A pond pump is an essential piece of equipment in a koi pond. It has one of the least glamorous roles to play, yet every healthy pond will be powered by a reliable pump. A pond pump has a most demanding job, working full time, 24 hours a day, and in most cases 365 days a year, often handling solid and undesirable matter in temperatures ranging from near freezing to perhaps over 25oC.

A good pump is one that is quiet, reliable, and easy to maintain and one that can almost be forgotten once installed. Often referred to as the heart of the pond, any pond pump (like our heart), must perform the most reliable function of a koi pond system. Because of its partnership with a pond filter, if a problem develops with a pump, then a problem is likely to follow in the pond’s balance.

Why have a pump? One pump:- many roles:

As koi ponds are generally stocked with fish above what is natural and self sustaining, the balance of the pond and ultimately the health of the koi are completely reliant on a filter system, which in turn must be fed continuously by a pump. Besides the obvious tasks of trapping or removing solids, a filter also performs the function of breaking down toxic waste produced by koi. These beneficial bacteria require a steady flow of water to supply them with food and aerated water and to remove their by-products.

Should a pump malfunction, or its performance be reduced, then the colony of bacteria would deteriorate leading to a similar deterioration in water quality. Whenever a pond does experience pump problems, be they a complete breakdown or a drop in performance, then the vital role played by a pump is self-evident, when koi can be seen sulking or gasping at the surface.

An additional function for the pond’s work horse is to circulate water through an ultraviolet clarifier. These algae-busting add-ons must be pump-fed to ensure that the unit runs at full-bore. Even though a UVC is not 100% efficient in flocculating all single celled algae in their first pass, their long-term relationship with a pump is essential for clearing green water.

If a large koi pond is fitted with a UVC, it is likely that all of the flow required for the filter will not pass through a potential ‘bottle-neck’ caused by a UVc or even a series of UVcs. For this reason, UVcs are often best run by bleeding off some of the flow from the main pump, or by using a smaller, completely dedicated pump for the UV.

Pumps can also be installed with a dual role of both water circulation and aeration, through the operation of a venturi. This is most applicable in a gravity-fed filtration system, where the chambers are installed alongside the pond, running at the same level as the pond. In the final chamber, where the water is at its cleanest, a submersible pump can return the water to the pond through the pond wall via a venturi. The pressure provided by the pump causes air to be drawn into the flow through the venturi, leading to Jacuzzi-like aeration of the upper layers of the pond. Besides performing the less glamorous functions of a pond, the pump can also perform aesthetic functions.

Although not as common in koi ponds as garden ponds, fountains can add another dimension to the life of a pond. With many different types of jet and fountain head to choose from, then there should be a fountain to satisfy your taste.

A more realistic role for a pump is to provide the life to a waterfall. More common in a koi pond that a fountain because of the need to use some of the spoil from the excavation as a feature, or to incorporate a pump-fed filter (which will in turn feed a waterfall). Either way, a waterfall requires a larger pump than if a water fall had not been installed.

Pump design

There are two types of pond pump available to the pond keeper – the external or surface-mounted pump and the submersible pump.

1. External pumps.

External pumps are sited outside of the pond. They should not get wet and are ideally installed in a small protective pump house. Water is sucked from the pond through a rigid suction pipe and pumped through to an external filter. These pumps are often referred to as swimming pool pumps and are better suited to larger, more specialist situations where above-average turnover of pond water is required. They are essential if a sand pressure filter is required as part of the filter system as they are capable of pumping to high pressures. Consequently, external pumps form a very minor part of the mainstream pump market.

2. Submersible pumps.

Submersible or internal pond pumps are by far the most popular pond pump. They are extremely versatile, being available in a range of sizes to suit most applications from a tiny fountain pump for a self-contained water feature to a jumbo submersible pump for a koi pond, filter and waterfall. They are very straightforward to install and having been developed in a very demanding market are sold with lengthy guarantees.

Despite some initial resistance when electric submersible pumps were first introduced to the pond market, their design is uncompromising when it comes to safety and they have an excellent safety record. The only moving part in a typical submersible pump is the magnetic impellor assembly which is driven by an electromagnet which is situated within the main pump body. All of the electric components within the body of a submersible pump are safely encased in hard resin which is itself retained in a robust and water-tight pump body.

The majority of submersible pumps are mains powered (220-240v) and can be plugged directly a mains socket through a ‘RCD’ breaker as an added precautionary measure. Some pump manufacturers also produce low voltage pumps which take their current from a transformer. These reduce the risk of a large electric shock within the pond, but present an additional problem of finding a safe location for the transformer.

Things to consider before purchasing a pond pump.

Before buying a pump, there are a number of vital pieces of information required to be able to make the ideal purchase.

1. The volume of the pond (including the filter system)

It is recommended that a pond system’s complete volume is turned over at least once every 2 hours. For example, if a pond has a volume of 3000 gallons, a pump capable of pumping 1500 gallons per hour would be suitable. However, most performance data provided by pump manufacturers will relate to performance in an ideal, blanketweed-free environment where restrictive pipework is not a problem. The work that a pump has to achieve in pumping water outside the pond, say to a filter and waterfall, will also have serious implications for the choice of the pump.

2. Work or ‘head’ that a pump has to achieve.

As soon as a pump has to move water vertically, the flow rate is reduced. The vertical distance between the water’s surface and the delivery height of the pipe is described as the ‘head’ with the greater the head, the lower the pump turnover. For example, if a pond has a volume of 3000 gallons, and requires a turnover of 1500 gallons per hour, if that same pond has a waterfall that is 3 feet high, then a suitable pump would be one that provides a turnover of 1500 gallons per hour (minimum) at 3 feet of head. This will mean choosing a larger pump than you may have first expected.

Furthermore, for a waterfall to look realistic, with the full channel width covered in flowing water, sufficient water must be delivered by the pump to the top. A flow of 500 gallons per hour is usually required for a waterfall 6″ wide and if a pump is not able to deliver this flow, then a waterfall will be a rather disappointing trickle rather than a cascading flow.

The advice when choosing a pump is the same when considering the size of a pond or filter: Always be inclined to opt for the largest one possible as it will provide your koi with a superior environment in the long run. A greater flow rate can easily be reduced, but if the pump is too small for the job, a new pump will have to be purchased.

3. Metric or imperial – Are you comparing like with like?

A factor of trading in the EU is that pump flow rates and volumes are more often measured and described in litres and minutes rather than gallons and hours. This can cause problems when comparing the performance of similar pumps, especially if your mental arithmetic is called into action in a busy aquatic shop! Be prepared to convert gallons to litres and vice versa when comparing the performance of a number of pumps. 1 gallon = 4.54 litres

4. The effect of pipework on flow rates.

Variations in pipework between different systems will have a profound effect on pump performance.

When piping water from a pump to a filter, use as few elbows as possible, tending towards the use of sweeping bends in flexible hose if possible. This will reduce the friction of the water in pipework, maintaining pump performance. Always use the pipe diameter as recommended by the pump’s manufacturer (even if reducing hose-tail adaptors are provided with the pump) as deviating from the ideal diameter will also reduce pump performance.

5. Power consumption.

As a pump is likely to be used continuously (especially as more koi ponds become heated), the running cost is a significant consideration when pricing up a pump for a particular task. Power consumption is measured in Watts with a greater figure relating to a power-hungry pump. The wattage will not always relate to the overall performance of a pump as efficiencies in design and construction can enable some lower wattage pumps to outperform pumps with larger motors. The difference in running costs over the lengthy lifespan of two different pumps could amount to the price of a new pump.

6. Guarantee

As a measure of how reliable (and competitive) pond pumps have become, most pumps are now sold with a free extended warranty of anything up to 3 years. With standard maintenance and the use of correct pipework so as not to produce high back pressures, then even these lengthy guarantees should easily be exceeded. Pumps are more likely to be temperamental if they are regularly switched on and off rather than used continuously and problems can also occur with pumps becoming blocked with debris or blanketweed, choking the impellor and leading to a burn-out.

Most pumps are fitted with foam or perforated plastic pre-filters to prevent impellors from becoming blocked, but these can reduce pump performance even when only partially blocked. More recently, pumps that will handle solids up to 10mm have become available on the market which are ideal for traditional weed-free koi ponds. Where a pump is situated in the final pump chamber of a gravity-fed system, then pump blockages should not be a problem.

7. Other desirable features

Many submersible pumps are fitted with additional safety features. Float switches are a safety back-up which prevents pumps from burning out should they run dry. Should the water level within a pump chamber drop, then the change in angle of the float switch will cause the pump to switch off. An additional safety feature found in many pumps is a thermal cut-out which also switches the pump off should it over heat. This will also protect the pump should it run dry.

In summary, a pump is an essential part of a koi pond system and it is crucial that it is purchased with a specific pond volume and head in mind. Many come with lengthy guarantees and efficient motors, which over a lengthy lifetime, could actually pay for the price of a pump compared with the running costs of alternative pumps.

Kill blanketweed and string algae.