You may think that a UV clarifier or steriliser isn’t necessary, or it can wait until later on after building your pond. And of course this is true, it isn’t essential for the running of your pond’s filter system. However it will enhance and improve your pond . UV is short for ultraviolet and is used to kill off the algae that makes your pond water green. This must be good for the fish mustn’t it? Well, yes and no. In actual fact, green water is actually good for your fish. It helps to protect them from over exposure to sunlight and contains high levels of natural nutrients.
Of course, that doesn’t mean to say that we, as fish keepers, want to maintain a nice green pond for our fish. We actually go to all of this expense of a fish pond so that we can enjoy their colours and watch them feed. Also, fish sometimes develop illnesses which need to be spotted as soon as possible, which is easier to do in good clear water. So we agree that a clear pond is the way to go and to do this we need to install UV.
There are two types of UV unit available:
- Kill off the algae that causes green water
- have no effect on reducing blanket weed growth
- A 50 Watt UV unit will cost at least £110
- Sterilise pond water
- kill up to 99.9% of certain viruses, algae, spores and bacteria
- have no effect on reducing blanket-weed growth
- Usually made form stainless steel, allowing UV light to be reflected inside the unit to improve performance
- Need matching to the flow rate of filter system
- UV sterilisers are larger than UV clarifiers
- Considerably more expensive – from £400 upwards
- Replacement bulb costs also significantly higher
Both types of UV unit expose the water flowing through it to ultraviolet light. The UV bulb is housed within a quartz tube, protecting it and the electrical connections from coming into direct contact with the water. Quartz is used as glass actually blocks some of the UV light from penetrating the water as it flows through the unit, whereas quartz does not.
UV units are installed on the pipework so that the water is pumped through it. Some filter systems have UV already built in to them. The position of the UV unit within the filter system is not critical except in pressure filters in which case it must be fitted after the pressure unit, otherwise the pressurised water may damage the unit.
So, before you buy a unit, you will need to know the water capacity of your pond. You will need 10 Watts of UV light for every 1,000 gallons of water. Think about where you will install your unit. Don’t forget, you will need access to mains power. Also bear in mind that most units are not waterproof and should not be installed anywhere liable to flood.
The UV bulbs will need changing at least once a year, and preferably every six months, regardless of whether they look clean and still produce light. The best time to change the bulb is March. This way, it will function at 100% throughout the summer months when green water is at its worst. UV light can damage your eyes so turn it off at the mains when you’re maintaining the unit.
When changing the bulb, take the opportunity to clean the quartz sleeve as they soon get dirty and limescale may have built up. You will need to remove the bulb to do this. Be very careful as they are fragile.