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How to install a UV light in a pond

Updated April 17, 2017

Installing an ultra violet (UV) light in your murky pond will help get rid of algae and harmful bacteria. This prevents the over-zealous algae from leaching oxygen from the water and killing your fish. Choosing the right UV light can be a daunting process, but with a little thought and consideration of your pond's needs, you can install a functional and easily maintained UV light on your own.

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  1. Learn how algae forms and how UV lights work. Algae are tiny plants that thrive on sunlight, warmth and nutrients in water. UV light destroys algae cell walls, causing algae particles to clump together. This larger size allows the filter to catch the algae more readily, thus clearing your pond.

  2. Decide the wattage of the UV light you'll need for your pond. You need a light bright enough to break down algae faster than it forms. The goal is not to prevent algae altogether -- that is impossible -- but to kill it faster than it can make the water green. Ponds up to 1,800 litres will require an 8-watt light, ponds up to 3,600 litres require 15-watts, up to 6,800 litres need 25-watts and up to 11,360 litres require a 40-watt light. More important to the function of your UV light is the pump rating. An inadequate light will not be allowed the time to clump algae when a pond pump is very powerful.

  3. Place the UV light in its desired location. Depending on the model this could be submerged or out of the water entirely. Either way, water has to eventually be sent through the light, by way of the pump's flow.

  4. Make sure you have enough hose-length -- and the right size -- to reach from the pond pump to the light chamber and then to the filter. If short, you'll either need to adjust the position of the UV light or buy more hose.

  5. Attach the hose from the pump outtake to the UV light chamber intake, then attach a separate hose from the UV light chamber outtake to the pond's filter. Nothing else will change from your original set-up.

  6. Tip

    If unsure what watt bulb you'll need, you can always overcompensate. A little more than you need won't harm your pond.

    Clean the waterproof sleeve protecting the lamp from water periodically. Build-up on the sleeve can reduce the UV light's effectiveness.


    Place the UV light in a moderately easy to access place -- you'll occasionally need to change the bulb. The bulbs are only effective from nine to 14 months.

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Things You'll Need

  • UV light

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