One of the most efficient filters you can use in your pond setup, especially if you keep fish, is a UV, or ultraviolet, filter. It consists of an in-line sealed box through which water passes. Inside the box is a second waterproof compartment that houses an ultraviolet light bulb. As water passes through one end of the box, past the ultraviolet light tube and out the other end, the light kills off algae--the water gardener’s sworn nemesis.

Didn’t I tell you this was a great filter?

Of several types of UV filters on the market, the most effective ones use a quartz filter sleeve to encase and waterproof the light. The intense light that a UV filter generates penetrates the walls of the algae (and other potentially harmful living organisms), causing them to die off and clump together. The clumps are eventually removed as they pass through your mechanical filter, which functions as a strainer.

The main drawback to using a UV filter is that it needs to run continually to be most effective, so a light bulb normally lasts for no more than a year or so. You should change the bulb and clean the quartz sleeve annually, even if the bulb still gives off light (the UV rays dissipate first, rendering the UV filter ineffective). While many pond owners replace the bulb every spring, if you live in a cold climate, you can replace it now. Since algae doesn’t grow very well in cold water, you don’t really need to run the UV filter in winter. By replacing the bulb now and keeping the filter off until the warmer weather arrives in spring, you’ll be all set to go once the algae starts to bloom next season!

One other thing about UV filters and algae: they don’t get rid of all forms of algae, such as the string types that cling to the rocks and sides of your pond. They get rid of only the suspended algae. But, since that’s the algae that makes the water appear green and dirty and robs the water of oxygen, killing off suspended algae will help keep your water clearer, cleaner, and safer for your fish.

UV filters have a coincidental benefit to fish ponds, as well. Just as they kill off suspended algae, the rays are also effective in eliminating many types of harmful bacteria, fungi, and parasites. That means a UV filter can benefit pond owners not only cosmetically by keeping the pond clean but also physiologically by keeping the fish healthier. Don’t believe me? Since adding a UV filter to our largest pond four years ago, our water has never been clearer or our fish healthier.

So if you don’t yet have a UV filter in your fish pond, think about getting one and installing it in-line soon. That way, when the warm weather arrives in spring, and the algae, bacteria, fungus, and parasites sprout like dandelions in the lawn, you’ll have one leg up on them. And your fish will thank you for it.

Guaranteed!