Choosing the right pump for your pond

Every pond should have one. Regarded as the heart of the pond, the pump (like the heart) must be the most reliable part of a pond and filter system. Expected to work 24 hours a day and every day of the year in most cases, the pump performs many functions, from the aesthetically pleasing through to the life saving. If a problem develops with the pump then a problem is also likely to follow in the pond.

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.

The external pump is sited outside of the pond, and water is sucked from the pond through a rigid suction pipe and pumped through to an external filter. These pumps are better suited to larger, more specialist situations where above-average turnover of pond water is required. 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 from a tiny fountain pump for a self-contained water feature to a jumbo submersible pump for a larger filter and waterfall. They are very straightforward to install and having been developed in a very demanding market are available with lengthy guarantees.

In the earlier years of water gardening and the advent of electric submersible pumps, there was quite a reluctance for pondkeepers to install such pumps amid fears of safety.

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 rotates in response to the magnetic drive produced within the main pump body by an electro-magnet. All of the electric components within the main pump body are encased in hard resin which is itself is retained in a robust and water-tight pump body.

The majority of submersible pumps are mains powered (220-240v), plugging directly into the mains 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 remove completely the risk of a large electric shock within the pond, but have an added problem of safely locating the transformer.

Pond pumps are centrifugal pumps, with the driven impellor ‘throwing water’ in an outward direction. (This force is experienced when standing on a rotating playground roundabout where we are thrown outwards unless we hold on tight!). As the impellor spins it creates a flow of water of some considerable pressure.

Pump Functions

The primary, life-saving role of a pond pump is to circulate the pond water through a filter. This action prevents a pond from becoming stagnant and by removing the solid and soluble waste, the filter allows more fish to be kept in a pond than would naturally be possible.

Ponds are generally stocked with fish to a level that is completely reliant on filtration, which in turn is only fed via a pump. The beneficial bacteria within a biofilter that break down the toxic waste produced by fish require the constant supply of food and oxygen that is provided in the pumped water. Should the pump malfunction, or not be run continuously, then the colony of bacteria would deteriorate leading to a similar deterioration in water quality.

A pond pump is also instrumental in the clearing of green water, by passing pond water through an Ultra-violet clarifier (UVc) which in turn burns the algae causing it to clump into filterable particles.

Pumps can be bought and installed for their aesthetic role. In self-contained water features, or pebble fountains smaller ‘fountain’ pumps are installed as purely a means of creating a pleasing effect of babbling water. Generally, when a pump is described as a ‘fountain’ pump, it will not have the capacity to lift water through pipework to a filter or waterfall. Standard waterfall or filter pumps are larger and must be purchased for the tasks of pumping considerable volumes of water to a height above the water.

Where a pump is installed in the final chamber of a multi-chambered filter that is gravity-fed, then a pump can also be used to aerate the water. Water that is pumped through an adapted pipework assembly called a venturi can actually cause the returning water to be injected with air. This causes the water to froth vigorously, aerating the upper layers of the water.

A final function of a pump is when it can be used to power a pond vacuum. If debris has settled on the pond bottom, then a pond vacuum which can be attached to the discharge end of a pump can be used to create suction through a pond vac, cleaning the pond bottom and removing dirty water simultaneously.

Things to look out for when considering 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 1000 gallons, a pump capable of pumping 500 gallons per hour is required. However, the work that a pump has to achieve in pumping water outside the pond, say to a filter, will also have crucial implications for the choice of pump.

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

Most pumps are sold with very flattering specifications, perhaps stating that a particular model will pump 1500 gallons per hour. This is probably measured at the pond surface without any restrictive pipework or fittings attached. As soon as a pump has to move water vertically, the turnover of that pump is reduced. The ‘head’ is measured as the vertical distance between the water’s surface and the delivery height of the pipe. The greater the head, the lower the turnover. Returning to the example, if a pond has a volume of 1000 gallons, it requires a turnover of 500 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 500 gallons per hour (minimum) at 3 feet of head, which may mean choosing a larger pump than at first expected.

3. What volume is required for a waterfall to look realistic?

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 useful rule of thumb is that an average running tap represents approx 200 gallons per hour. A flow of 500 gallons per hour is usually required for a waterfall 6″ wide. If a pump is not able to deliver this flow, then a waterfall will be a trickle rather than a cascading flow.

4. Metric or imperial?

Pump flow rates and volumes are more often measured and described in litres and minutes rather than gallons and hours. Be prepared to convert gallons to litres and vice versa when comparing the performance of a number of pumps. 1 gallon = 4.54 litres

Tip. If in doubt, always choose a slightly larger pump than may be required as a greater flow of water can easily be reduced, but if the pump is too small for the job, a new pump will have to be purchased.

5. The effect of pipework.

Although a pump’s performance may be rated at say 500 gph at 3 feet of head, this will not take into account variations in pipework which can have a profound effect on 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 reduce turnover. When piping water from a submersible 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.

6. Power consumption.

As a pump is likely to be used continuously, the running cost is a significant consideration when pricing up a pump for a particular task. Power consumption is measured in Watts with the greater the figure relating to a power-hungry pump. The wattage does not necessarily relate to the overall performance of the pump as many efficiencies in design and construction enable low wattage pumps to outperform pumps with larger motors. For example, when comparing 2 pumps each rated at 500 gph, one may be a 65W model while the other one may be a 100W model. Which would you choose? The difference in running costs over the years could amount to the price of a new pump.

7. Guarantee

Most pumps are now sold with a free extended warranty of anything up to 3 years. This is a measure of how reliable (and competitive) pond pumps have become. With standard care and the use of correct pipework so as not to produce high back pressures, then such guarantees can easily be exceeded. Pumps are likely to be more temperamental if they are 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. Self-cleaning pre-filters are available as a remedy for this common blocking problem and for larger pumping jobs, pumps that will handle solids up to 10mm are readily available on the market.

In summary, a pump is an essential part of a 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.