UV Pond Filters Fight Different Algae Types

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Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

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By definition, a uv pond filter is actually a combination of several different technologies put together in a single package. UV, or ultra violet light is actually not a filter at all, but when it’s combined in a system that also contains a biofilter, you’ll find this array to typically be referred to as a uv pond filter.

This type of system is becoming more popular for small pond owners because it integrates two commonly used, but different systems for algae control. Historically uv light and bio filters may both be installed in a pond but these new, pre-integrated units make sizing and installation a bit easier.

Let’s discuss the components of the pairing and some of the benefits they bring to the pond owner.

The UV Sterilizer Light

The UV light which uses ultraviolet light waves to, in a sense, clarify or sterilize the pond water, is charged by a quartz light and when operating correctly it will damage single cell algae and kill bacteria and viruses. It’s indiscriminate in what it damages but many koi fish owners prefer these systems because they do help to control some viral pathogens.

UV is particularly well suited to helping with green water problems. This tinting which can run from very light to a very think, dense appearance is made up of single cell algae that is free floating in the water. As their density increases, the color will become less transparent to the point where you may not be able to see more than a few inches into the water.

The planktonic algae is damaged somewhat as it passes in front of the uv light and this makes these very small cells clump together. As these masses accumulate in size they will be more easily filtered out by either a bio or mechanical filter.

UV, if it’s set up correctly, namely that the flow rate of the water through it correct, as well as how frequently the entire water volume of the pond passes in front of the light (see manufacturers suggestions), it can reduce green water problems quite quickly.

But why is flow rate so important?  Well, if the water and algae are traveling too fast through the UV, it will not get exposed long enough to possibly do damage.  A slower flow rate would normally provide better control.

In most cases, pond pumps are designed to provide a circulation rate of the full gallon volume of a pond, once per hour.  Have a large waterfall installed, may change this rate somewhat, but overall, when sizing a UV to the pond, you can use the pond volume of course, but a better method would be to use the GPH (gallons per hour) rating on the pump, and exceed that number.

Most UV makers will provide a wattage to GPH, or pond size comparison that you can use to fit the ultraviolet device to your pond.

One final important note regarding uv and algae control is that it will not work at all on string algae problems, or any type of algae that can’t pass through it. If it’s not exposed to the light, it will be unaffected.

The Biofilter

In the basic design, biofilters are actually a combination of a mechanical pond filter, which uses mesh or foam screens, along with a biochamber, which holds some form of media that supports and sustains beneficial bacteria. This bacteria is the “bio” or biological component that helps to keep the biofilter functioning and processing the material that get’s captured in it.

The media that holds the bacteria may come in the form of foam pads, coiled strands of plastic, balls or spheres, or cubes. Anything that can provide a save haven and home for growing bacteria is usually good.

This media will also help to trap or capture elements in the water that are intended to get filtered out. Nutrients from fish waste such as nitrites and other organic materials, as well as particulates and cells of algae may get trapped and processed. Anything that’s organic in nature can be “eaten” or assimilated by the bacteria. Inorganic material such as sand grains would simply sink to the bottom of the chamber.

Virtually any pond with fish will want to use a biofilter because they help to keep not only nutrients in check (which can lead to algae growth) but they also stop ammonia and nitrites from building up in the pond water. They are a part of what’s called the nitrogen cycle where these dangerous elements are naturally broken down into harmless substances that are then readily available to support desirable pond plants.

Biofilters work best when water is continuously run through them without much interruption. If the water flow is turned off for very long, bacteria begins to die off and the filter becomes less effective in it’s work. It’s suggested to supplement this work by adding beneficial bacteria to the pond from time to time to keep the filter well primed. (Editors note: It’s advised to turn off the uv light for at least 24 hours whenever you add bacteria into the pond. This gives it time to build up and accumulate in the biofilter)

The Pros And Cons Of A UV Pond Filter

When UV lights and biofilters are combined, the end result is a UV pond filter. For many pond owners these work very well and are easy to install. In some cases however, such as if the pond only has issues with string algae, the pond owner may want to turn off or disconnect the uv light for a time to see if things improve. UV is worthless on this type of algae anyway but at the same time it can damage some beneficial bacteria which will work on string algae. Most of these combined units will still allow you to disable the uv if necessary.

It’s also important to make sure your uv light bulb is replaced from time to time. The effective working life of most bulbs is around 12 to 14 months of continuous operation. This will vary a bit depending on the brand but all of them become less effective over time and should be replaced.

All in all, nearly every pond will benefit from a biofilter. UV light is a very good option for those that tend to have chronic problems with green water, or if the koi owner has concerns about viral control.

As with any other mechanical addition for your pond, be sure to do a fair amount of research to insure that you find a unit and model that will be best suited to your pond size in terms of gallon volume as well as your anticipated fish loading. Doing so will provide the best results with a UV pond filter.

Below you’ll find some examples of the bio filters as well as the integrated UV/Filter combinations.  The key, as always, is to select a filter that will exceed the gallon volume of your pond.

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