What pumps to use?

This is the second most important decision you will make in the conversion of your swimming pool to a Koi or fish pond. Your pump is the heart of your filtration system as it moves the life blood (the water) of your pond to the filters which clean and purify the water before returning it to your pond.

As with all Koi ponds the pump will be operating 24 hours a day, 365 days a year. As such an important decision has to be made in respect of reliability, running costs and ease of maintenance.

Most pumps operated to manufacturers specifications these days are reliable. Pumps failures tend to be traced to situations beyond the pumps' control such as when they have been running dry without water to cool them for several hours. This is normally fatal to a pump, despite most having built in thermal cut outs.

You should only consider pumps rated for continuous use, so beware of these so called sump pumps that are often misused in Koi ponds. Sump pumps are designed for on off operation and if run continuously they typically exhibit a much shorter working life than a purpose built submersible.

The running costs of a pump are also significant to consider when one takes into account that now they are going to be running 24 hours a day. Your swimming pool pump that is currently attached to your pool might at first glance appear to be an appropriate pump but in reality, despite it's already having been paid for attraction, it is probably not the correct pump for your pond.

Swimming pool pumps generally are self priming high pressure pumps that are able to deliver copious quantities of water under pressure to a sand filter. They are also able to deliver sufficient suction to drive a pool cleaner device but the downside is that they chew through a lot of power to do so.

In a Koi pond such power is simply not necessary from your pump. A 250W submersible pump can compare quite favourable with a 750W swimming pool pump in terms of water delivery volumes. In other words the flow rates through your filter system will be roughly similar but using only a third of the power. 

Depending on the size of your pond, you should be aiming at turning water over through your filters once every two hours. Once an hour is better if you have a smaller pond and of course if you are planning to stock your pond heavily (say at  one fish per 1000 litres, which is the maximum rate we recommend) once an hour turnover rates would be considered a minimum.

Our belief is that it is better is to stock at a rate of one fish per 2000 litres in a converted swimming pool and aim at a turnover rate of once every two hours.

This will determine the flow rates that your pump will need to deliver. Typically most pumps will manage to deliver around 75% of their stated outputs in real world situations once you have accounted for flow rate losses owing to the friction losses of pipes, bends, valves and such like.

Submersible pumps have the advantage of being silent. They have the disadvantage in that they are unsightly and can be more difficult to hide as opposed to a more simple slotted pipe. Of course submersible pumps can be hooked up to slotted pipes and this may afford you more opportunity to locate the pump elsewhere in the pond where it is not as obtrusive. Once again, the sky is the limit to your ingenuity.

On this note, a word of caution. Be careful to ensure that your pump doesn't suck up larger debris, such as leaves and twigs, that can become entangled in the impellor of the pump. Or, and trust us on this, you will be forever pulling the pump out, opening it up and cleaning out the impellor so that it can spin unimpeded once more.

There are many submersible pumps now on the market that sport clamshell type housings that prevent exactly this from happening. Hailea makes such a pump and Oase also make an excellent, if somewhat more expensive, version.

No matter what submersible pump you opt for, make sure that you install it with a union

50mm Union

on the pipework so that you can simply undo this union and pull up the pump to maintain it quickly and easily. Try and install the union above water - undoing a union in freezing cold winter water that is covered in algae and slimy bio film is a simply soul destroying exercise that does not come recommended. 

Never pull the pump up by its power cord. This is asking for trouble and repeated such offences will lead to the power cord becoming frayed and eventually shorting into the pond. This can cause discomfort for your Koi and can kill or maim them. Not to mention costing you a new pump in the process.

External pumps also come in many different shapes and sizes with varying efficiencies. The most popular are the swimming pools pumps which are generally extremely rugged pumps. They work for years on end and can pump massive quantities of water under some impressive pressure. Their drawbacks lie in their running costs, and in the fact that they are noisy.

Swimming pool pumps are less sensitive to impellor blockages however and most of them sport leaf traps built in the front of the pump that ensures they do not get clogged. Spare parts are also generally easily available for these pumps as there are a truly massive quantity of them already installed.