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UV Clarifiers for Ponds: When to use them and how to pick out the right one

aqua ultraviolet uv clarifiers displayed over a pond image

Ultraviolet lights are most commonly used in a koi or backyard pond to get rid of that dreaded green, pea-soup colored water. The pond uv lights are used in a product called UV Clarifiers that kill single celled organisms in water as it passes through the systemís chamber, ultimately serving as an enhancement to a pondís filtration system.

While UV pond clarifiers are namely used for clarification they can also be used for advanced sterilization with the right flow rate. The reason they are so often used for getting rid of green water is because they are all-stars at destroying single cell algae, the main perpetrator of green pond water.

Do all ponds need UV Clarifiers?

If you have green water and have already tried correcting it with water treatments to no avail then a UV Clarifier is just what the doctor ordered. Not all ponds require UV clarifiers, but they can help clear and prevent green water better than any other product on the market. If you have a pond with less than 50% shade and find yourself constantly fighting green water then we highly recommend adding UV. We also find that experienced pond owners appreciate using UV to not only keep water clear but to provide further sterilization on the quest for the healthiest water possible.

Pro tip: If youíre building a new pond or looking to also replace your filter we suggest adding a filter/uv combo for guaranteed clarity.

How to pick out a UV Clarifier for your pond

UV clarifiers can be purchased separately or as a part of a Filter/UV combo. If you already have a pond and a filter setup youíll likely want a stand alone unit (unless youíre looking to also replace your filter). If you donít have a filter yet the Filter/UV combo options are popular because of the all-in-one feature.

stand alone unit and combo unit
Stand alone UV Clarifier (on left) and a Filter/UV combo unit (on right)

Stand Alone Units

There are three main factors that need to be considered when selecting a UV clarifier for your pond:

  1. Pond size
  2. Pump flow rate
  3. Pipe material

First, you need to calculate the gallons in your pond in order to select a clarifier that can handle your pond size. Every UV unit will note a max pond size and max flow rate it can serve. So next, you need to also understand the flow rate of water cycling through your filtration system. If your flow rate is higher than a particular UV clarifier can handle then it will be ineffective.

In general, we suggest picking a UV clarifier that has a max flow rate at or below the max flow rate of your actual pump. If you donít remember the max flow rate of your pump the easiest way to find out is by finding the product on our website and checking the specs (if itís a pump we carry). If you have a pump that we donít carry then a quick Google search should do the trick. Max flow rates should be listed on manufacturersí websites, too. We list max flow rate on all of our pumps as GPH (Gallons per hour).

Finally, to select a UV Clarifier that will work with your pond configuration you need to consider the pipe material. Some clarifiers are manufactured to fit PVC piping while others are made for barbed fittings (think vinyl, rubber or kink-free tubing and hose clamps). There are even a couple of clarifiers that are made to fit inside specific skimmersóthis can be especially helpful for ponds with hard to reach piping. Read product descriptions closely to be sure a particular clarifier will fit to your pipe type and size.

Aside from these three main factors, the remaining options to consider are based on your preference: such as whether you want a UV clarifier with a plastic housing or an upgraded UV clarifier with stainless steel.

Filter/UV Combo Units

The same factors that apply to the stand alone UV units need to be considered when selecting a pond filter with UV light (a Filter/UV combo unit). Of course, youíll have factors to consider for the filter, too.

Best UV Clarifiers for PondsóOur Recommendations

All UV clarifiers and filter/uv combos that we carry are quality products. We donít sell anything that we canít stand behind, but our Pond Techs do have favorites and those that they consider the best performers.

For stand alone units, the line we most highly recommend is Aqua Ultraviolet. This company specializes in UV lights (itís what theyíre known for), and their UV clarifiers are extremely reliable. They have a variety of options including Classic units (our best sellers), stainless steel units, units that have wipers for easy quartz sleeve cleanings, and units that will even handle up to 150,000 gallons of pond water.

For those looking for a quality, cost effective unit, we recommend the Tetra pond UV Clarifiers.

For filter/UV combos we highly recommend the Laguna, Aquascape or Oase pressurized filters with built in UV.

Installing a UV Clarifier

Most stand alone units are external inline units, meaning they get installed inline with your piping outside of the pond water. There are a few submersible uv lights for ponds as well. In order to install the UV clarifier inline with your pond piping you will need to cut the piping and fit each end of the unit to either side of the pipe you cut so that after the job is done the UV clarifier essentially serves as a continuous part of your piping.

Before you cut your piping you will need to make sure the water source for the area of pipe you are cutting is either redirected with valves, or if thatís not an option youíll want to turn off your pumpís power source.

Also it's important to place the uv light after your filter when installing a stand alone unit. This will inhibit debris from entering the UV chamber (like a small stone, which could damage the internal glass).

The installation itself usually only takes about 5 minutes.

Installing a filter/uv combo is a similar process but will vary based on the filter you select.

illustration showing uv clarifier parts
In this example UV Clarifier, the bulb and connections have been pulled out of the unit's chamber to illustrate all parts. To assemble the lamp is pushed inside the chamber and all caps, connectors and seals are secured. Pipes are fitted to the ends highlighted in the illustration.

When to Run UV

Once you have your unit installed we recommend keeping it running 24/7 with just a few exceptions.

If you live in a climate that gets cold, definitely shut your UV off and winterize, or bring it entirely indoors when the temperature nears freezing. You donít want water to freeze inside the unit which can cause irreversible damage.

Also, turn your unit off for a few days when treating your pond with beneficial bacteria to give the good bacteria a chance to hunker down where itís going to live. UV clarifiers donít discriminate between good and bad bacteria, so itís likely your good bacteria would be killed if passed through an active UV chamber when first getting added to a pond.

What to Expect after Installation

On average, if everything is sized properly and you have adequate shade, most manufacturers state that you should see results about 7 days from the time you turn on your new UV.

Many units (both stand alone UV clarifiers and those in the filter/uv combos) have indicator lights to assure you that the UV light is on and doing its job. If the light is on and all systems are a go, the only other yearly maintenance will be replacing the lights every 12-14 months (of run-time).

UV Clarifiers for the Win

With the proper UV clarifier you can both prevent and eliminate unsightly green pond water. These little lights are powerful agents that allow pond owners everywhere to have crystal clear water and enjoy living the pond life to the fullest.

Article Posted: 02/08/2022 10:30:50 PM

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