How to Troubleshoot a UV Pond Light

Ultraviolet lights are often used with a pond filter to kill pond algae. They work well at killing most algae and will keep the water crystal clear. The UV light is sealed off from the water and is installed as a part of a filter out of the water. The pond water is pumped through the filter and is pumped past the UV light, so the ultra violet light rays hit the water and sterilizers it, killing the algae. If your water starts turning green and your UV light appears to not be working, here's how to find out what could be wrong.

Checking your Lamp

  1. Make sure your light is on and not burned out. If it is not lit up, you either have a burned out bulb, a bad ballast or an electrical problem. Chances are it is a burned out bulb, so order and install a new one.
  2. Check your electrical source. If you have to, plug in another appliance to make sure it is working. If If the appliance does not work, you have an electrical problem. Check your circuit breaker box first. If you can see no problem there, call an electrician.
  3. Decide how old the lamp is. Most ultraviolet lamps have a life span of nine to 12 months. If yours is older than that and is not glowing, chances are you need to change it.
  4. Find out if your ballast is bad. It can go out because of flooding, lightning or power surges. If these things have happened at your house lately, you may need to replace the ballast.
  5. Clean the sleeve. There is a sleeve that protects the lamp from the water. It can get dirty. That sleeve is usually made or quartz and is very expensive. Be very careful while cleaning it. Use the paper towels and vinegar to clean it.
  6. Check the placement of pond equipment. Your pump should be as far away from the UV sterilizer as possible. Put your submersible pump at one end of the pond if the UV light is at the other. If the pump and the light are close together, all the water is not circulating through the light and getting sterilized.

Things You Will Need

  • Paper towels
  • Vinegar


  • A UV light can make your pond viewing much more enjoyable. It does keep the water from becoming green.


  • A UV light is a luxury, not a necessity. It does not make your water healthy. You still need a balanced pond for ultimate water health. A balanced pond has one bunch of submerged vegetation per square foot of surface area, at least one half of the top of the water covered with floating plant material, no fish feeding, therefore no koi in your pond, and one linear foot of goldfish per 25 square feet of pond surface. If you have koi, you cannot have a balanced pond because you must feed your koi. A UV light is perfect for the koi pond.
  • Remember, just because the water is clear does not mean it is healthy.
  • Always use a GFCI (Ground Fault Circuit Interrupter) electrical outlet. The GFCI will cut off electricity instantly if water touches it.
  • An ultraviolet light will not kill string algae or blankeweed.

About the Author

This writer has been at the writing craft for over 50 years from long before computers or even electric typewriters. Now retired from her day job she spends retirement hours writing for online sites.