Can A UV Pond Filter Control Algae?

Photo of author
Written By Mark Washburn

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

Pond Talk is an Amazon Associate. As an Amazon Associate we earn from qualifying purchases.

A UV pond filter may be one of your very best options at controlling algae in your small pond or water garden. UV or ultraviolet light is touted by manufacturers as a very good tool for algae control but some of the claims need to be clarified to ensure that this type of device will actually help you with your current problem.

First of all, a UV pond filter is not really a filter at all. It’s simply a tube that contains an ultraviolet light and in terms of algae control it will help on many types of single cell or planktonic algae. These most often present themselves as green water in a small pond. In small numbers they are not often even noticed but as they multiply, the water will get a darker and denser color of green. Some of these algae may also have tints of red or a blueish green.

Many pond owners find this type of algae to be very stubborn and even when treated with something like an algaecide, or a full pond cleaning and water change is done, it’s not unusual to see the green water come back within a matter of days. If this is the case with your own pond, then a uv light is worth investigation. Using radiation waves, ultraviolet light will damage or kill most organisms that pass through the light. UV is fairly indiscriminate of what it will kill and the list includes bacteria, viruses, algae cells, and other microorganisms.

It should be noted however that when claims are made regarding complete algae control in a pond, UV is not a complete solution. String algae which is another common problem will not be affected by a UV pond filter simply because it can’t pass through the tube and be exposed to the light. Other options exist for sting algae control but UV isn’t one of them.

To get the best results with UV sterilization a couple of things need to be kept in mind. First, be sure to use a system that’s more that adequate for your pond’s gallon volume. Do not try to cut corners and go with something too small. Ideally the full gallon volume of the pond should pass through the UV pond filter at least once per hour. This consistent exposure to the light will improve it’s effectiveness. Also the flow rate of the water through the tube needs to be correct based on the manufacturer’s suggestions. A flow rate that is too high will allow the water and algae to pass through the light too quickly. A slower rate is more ideal in that it provides more time for the algae to be damaged by the light.

Single cell algae is either killed or damaged when irradiated. Normally this makes these very small cells clump together which provides easier filtering with either a mechanical or biological filter. The latter is particularly useful with a uv light because bio filters are somewhat self cleaning and also help to manage organic nutrient loads such as nitrates, nitrites and by products such as ammonia.

Most uv pond filters don’t require a lot of maintenance however the light should be changed after 12 to 14 months of use. Although they may still emit light, the effects of the radiation may become diminished after this time. To be sure, consult with the owners manual and the manufacturers suggestions on how often uv replacement bulbs should be changed.

For many koi pond owners, green water problems can become a thing of the past with a uv pond filter is installed and operated correctly.

Amazon and the Amazon logo are trademarks of, Inc, or its affiliates.