Delaware Custom Ponds LLC

To answer this question, we must first understand what UV sterilizers do (and don’t do). UV sterilizers sterilize. A strong ultraviolet light is used to “burn up” everything living in your water that is directly exposed to it- most visibly planktonic algae (phytoplankton) but also all the associated zooplankton as well. Most zooplankton is harmless and feeds off of phytoplankton or other zooplankton, but a few kinds of microbes that may be in your water to some extent are dangerous to our fish such as aeromonas, pseudomonas, and parasitic ciliates. Some viruses may be killed by UVs as well, but effectiveness is less well documented. In order for the UV light to work, it must be sized correctly and exposed directly to all of the pond water at close range. In-line UV sterilizers are connected directly to your plumbing to ensure that all the water passing through the particular pipe is exposed. Drop-in UVs can be thought of as lamps that radiate ultraviolet light all around them and are typically placed in high flow chambers within your filtration like skimmers or waterfall boxes. They are not quite as precise as in-line UVs, but if properly sized can do the job almost as well.

So now that we know what UV sterilizers do, when do we need them and when don’t we? If any of the following applies to you, then a UV would be helpful. Your pond is heavily stocked, high in nutrients, low in aeration, has low alkalinity, and/or your fish are less than perfectly healthy. Under these conditions, clearing up the water and everything living in it is helpful in stabilizing pH, ensuring adequate levels of dissolved oxygen at night, and ensuring that you can monitor your fish for health purposes.

However, if none of the above risk factors apply to you and your pond, then a UV probably isn’t necessary and the color of your water is purely a matter of cosmetics and personal taste. In fact, there are some drawbacks to using UV sterilizers if they are not needed. Firstly, it’s important to understand the UV’s kill floating algae, they don’t remove nutrients. All that dead water column algae breaks down in your system and releases the associated nutrients, which can then lead to the dreaded (and often more problematic) hair algae taking over. Also the phytoplankton/zooplankton soup that your UV kills actually forms the base of a natural food chain that feeds fish fry and beneficial pond critters, which themselves provide free high quality forage for your fish. Also, while you may or may not like the look, “colored” pond water provides shade for your fish (yes koi can get sunburned), protection from predators, and consequently reduced fish stress.

Ultimately, the choice of whether to add and use a UV sterilizer comes down to your personal preferences and system characteristics. It’s even possible that a UV may be beneficial to a pond some times of year and unnecessary for others. We typically install them on new koi pond builds that the client can do with as they please, but they’re also easy enough to add in afterwards in most cases. Bottom line though, as with any other single piece of equipment, a UV sterilizer is only as good as the overall system it is incorporated into and isn’t the “miracle cure” it is sometimes made out to be.