Koi

When building a Koi pond there are some things that you must have, like a pump and a filter. On the other hand, there are items which aren’t absolutely necessary but will enhance and improve your Koi pond – such as a UV unit. UV is short for ultraviolet and is used to kill off the algae that makes your pond water green.

Green water is actually good for your Koi because it protects them from overexposure to sunlight and contains high levels of natural nutrients. Despite the benefits of a naturally green pond, most of us keep Koi to enjoy their colours and to watch them come up to feed; these things simply could not be appreciated in a green pond. Along with this is the fact that, unfortunately, Koi do develop illnesses which need to be spotted early – obviously clear water will allow you to do this more easily than if the pond is green. There are two types of UV unit available:

UV clarifiers
• Kill off the algae that causes green water – although they have no effect on reducing blanketweed growth
• A 50W UV unit will cost around £110

UV sterilisers
• Sterilise pond water, and could kill off up to 99.9% of certain viruses, algae, spores and bacteria – although they have no effect on reducing blanketweed growth
• Typically made form stainless steel, which allows the UV light to be reflected inside the unit and improve performance
• Must be matched to the correct flow rate for optimal functioning
• UV sterilisers are larger than UV clarifiers, and considerably more expensive – from £400 upwards
• Replacement bulb costs are also significantly higher than that of a standard, clarifying UV unit

A typical UV unit, be it a clarifier or steriliser, exposes the water that flows into the unit to ultraviolet light. The UV bulb is housed within a quartz tube to protect the bulb and the electrical connections from coming into direct contact with the water, because glass actually blocks some of the UV light from penetrating the water as it flows through the unit, whereas quartz allows for a higher level of penetration.

A UV unit is installed on the pipework so that the water is pumped through it. Some filter systems are even available with an integral UV filter, but these are more commonly fitted to pump-fed ponds.

In most instances, the position of the UV unit is not critical; but you should always fit a unit after any pressurised filtration equipment as the pressurised water may damage the unit.

Before you buy…
• What is the gallonage of your pond?
• How much exposure to direct sunlight does the pond get?
• You will need 10W of UV light per 1,000 gallons of water
• Where will you install the unit (you will need access to mains power)?
• Most units are not waterproof and should not be installed anywhere liable to flood

Maintenance
UV bulbs should be changed at least once a year or every six months, regardless of whether they are still producing light. The best time to change the bulb is March; then it will be functioning at 100% throughout the summer months when green water will be at its worst. UV light can damage your eyes so turn it off at the mains when you’re maintaining the unit.

At the same time as changing the bulb you could also check the quartz sleeve to see if this needs cleaning, especially if you live in a hard-water area as limescale may have built up. You will need to remove the bulb before cleaning it – use a soft cloth and take extra care to avoid any accidental breakages. In the unlikely event that the unit is not working, always check the quartz sleeve first – if this is intact, you may need to replace the starter (if your unit has one) or it may be that a new starter ballast is required. In many cases, it may be a more cost-effective solution to replace the unit.

Written by Keith Holmes