Last Updated: 1/14/09

Introduction
Installation
Maintenance
Pros
Cons

Be sure to visit the main pond algae page for a ton more information!

UV sterilizers can be used to kill suspended algae. They will also damage or kill any microorganisms, bacteria, viruses, etc. that pass by the light. I do not have a ultraviolet sterilizer but I thought I would list here what I believe are some of the pros and cons of adding one to your filter system. UV sterilizers or UVC's (for ultraviolet clarifier) kill living organisms including algae, animals, bacteria, viruses, etc. that pass by a UV bulb. To be killed, something must pass by the bulb and at a slow enough rate to be effected.

Most systems I have seen place the UV sterilizer at the start of the filtration process. I disagree with that. The cleaner the water is when it passes by the UV lamp, the more relative impact the rays will have on suspended green algae. Also, any small animals, plants, debris, etc. that come by the lamp will reduce its efficiency not to mention kill any such small animals. The UV lamp should therefore be after the mechanical filtration. It should also be after the biological filter if possible. This will make it easier for good bacteria to get into the biological media as the UV rays will kill the good bacteria as well as bad. If placed before the media for example, if a commercial preparation of good bacteria is added to the pond to help seed the biofilter, those bacteria would be killed by the UV before reaching their new home.

The bulb should also be placed where it will not get wet (above pond level if possible) and where it is easy to maintain.

UV lamps should be changed routinely, normally once a year, often at the spring start up. The age and cleanliness of the bulb effects its output. If the bulb has anything on it, that will block the UV rays from leaving the bulb to do their work. Bulbs that become really dirty can be cleaned with a dry or slightly damp clean cloth but only after the bulb is off and cooled. Even fingerprints on the bulb will reduce its efficiency so only handle the lamps by the ends. The UV lamp should be put up over the winter to reduce the chance of freezing or cracking.

Advantages

• Kills suspended algae, and then you can actually see the bottom of the pond!!
  
• Kills bad bacteria, viruses, parasites, and other pathogens that pass by the light.
  
• Saves fish from the above so the fish are healthier.
  
• Due to the demise of algae, provides more nitrate and other nutrients for the higher plants.
  
• Due to the demise of algae, provides more light for the submerged plants to grow and flourish.
  
• Provides higher visibility which allows the earlier detection of injured or sick fish, dead plants, holes in the liner, upset pots, and other problems.
  
• Provides greater enjoyment of koi, goldfish, etc. due to the increased visibility.

Disadvantages

• Kills good nitrifying bacteria that pass by the UV so it must be shut off during spring to allow bacteria to get started and whenever there is a die off of good bacteria.
  
• Kills good insect larvae, tadpoles, fry, daphnia, paramecium, other microorganisms, and whoever gets sucked in. This is the main reason I do not have it since I want all the small animals for a balanced natural pond. Providing good mechanical filtration before the UV prevents the larger of these animals from being zapped.
  
• Decreases oxygen. Initial start up of the UV would result in death of algae that would decompose creating a decrease in oxygen and an increase in hydrogen sulfide.
  
• Promotes growth of attached algae. Without the suspended algae's removal of nitrate, a nitrate spike would result in a fast growth of attached algas like hair algae which could clog filters.
  
• Via death of microorganisms and insects, deprives higher organisms (your fish) of a vital natural food which improves their overall health and breeding.
  
• Costs a lot. UV's cost a lot of money initially ($150 to $500), a lot to run (electricity), and a lot for replacement bulbs.
  
• Opens up pond animals to higher predation rates. The higher visibility of the fish makes them easier targets for predators such as herons and raccoons.
  
• Has little or no effect on decreasing attached algae like green algae and hair algae.

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