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Do I need a UV Filtration system for my pond? – Decorative Ponds & Water Gardens Q & A


Do I need a UV Filtration system for my pond?

Do I need a UV Filtration system for my pond? Benjamin – Dover, DE

Make Your Green Water Head Towards The Light

Spring is in full effect, the sun is shining, trees everywhere are in bloom, but now your pond water is as green as the grass that surrounds it. The water in your pond may have started off crystal clear this season but was it too good to last? Here at The Pond Guy we think not! If you can’t seem to gain the upper hand in your fight against green water it may be time to break out your secret weapon, a UV clarifier.

Some of you may be scratching your head at the idea of exposing your pond to even more light, but the truth is, when properly implemented, a UV bulb can work wonders on improving your pond’s water quality. The principal behind UV clarification is simple; expose algae to concentrated UV rays to damage and ultimately kill the plant. The trick to getting the best results from your UV clarifier is to pick a bulb that has a high enough wattage for your ponds volume and to pump the water past the bulb at just the right flow rate. All UV clarifiers are rated based on pond size. The larger the wattage, the larger the pond size the UV clarifier can handle. The other factor to take note of is the pump size. Pushing water past the UV light too fast can render it ineffective while pushing the water too slow can cause the UV Clarifier to act like a sterilizer, killing not only algae, but your beneficial bacteria as well. A great rule of thumb here is to push the water approximately half of what the UV is rated per hour. For the Tetra 9-Watt UV Clarifier that is rated for ponds up to 1,800 gallons a 900 GPH (gallons per hour) pump would be ideal.

The continued success of UV clarification has brought about many new styles of UV units; if you are currently building a pond consider purchasing a skimmer like the Savio Standard Skimmer which comes with optional built in UV. If your pond has been up and running for years you can use a Tetra GreenFree® UV Clarifier which installs in line with your plumbing, or the Pondmaster® Submersible UV Clarifier which can be plumbed in-line or submerged directly in the pond. There are even pressurized filters like the AllClear™ PLUS Pressurized Filters that come with a built in UV clarifier. Each type of UV is available in multiple wattages to best fit your specific needs.

While a UV clarifier can work wonders on your water garden it is only a patch to the real issue. Make sure you are properly maintaining your pond, using an adequate amount of filtration, and utilizing your bacteria products in your DefensePAC®.

If you are unsure on How To Create A Balanced Environment for your water feature, or need to brush up on your Filtration Basics you can learn tons of tricks and tips on our Blog page.

Pond Talk: Which type of UV clarifier do you use in your pond? Has it made the difference between a pond full of “pea soup” and a crystal clear water garden?

4 Responses

  1. First time pond builder. Digging a 5w x12 long pond avg depth 2 feet. 1 foot at shallow end 3foot at deep end. Have liner donated by local billboard company with old truck bed mats as side walls under the liner to protect against roots. The water fall will be about 2.5 feet from ground to water stream point. It will have 2 small shelves 3″ and 4″ wide respectively. I have a 4000 gph pressurized filter with a 13 watt UV light. I also have a 2100 gph pump which I am told by salesmen is way to small and that I also have to invest in a skimmer. Can you give me some advice without the sales pitch?

    • Hi Michael – There are several factors to consider when selecting the pump size needed for a pond. Let’s do a little math first and calculate your water volume. 5 ft x 12 ft x 2ft avg x 7.48(#of gallons in cubic foot) equals approximately 900 gallons of water in the pond you are constructing. General rule is that you want the pond to turnover once every 2 hours so you would need a pump around 1800-2000gph to accomplish this. Another other factor that affects pump size is the width of the waterfall. 1500-2000gph per foot of width will give you a steady flow. If your waterfall is only about 2.5 ft tall and no more than 10 feet of distance between the pump and waterfall you will have about 3.5 ft of head pressure so as long as your 2100gph pump will produce the correct volume needed at 3.5ft head pressure then you are fine. The final factor is how the pump interacts with your filter. All filters have a maximum flow rating that they can handle. This is especially important with a UV filter. Pushing the water through to quickly can harm the UV and cause leaking, too slow and it may not turnover the pond fast enough. You will need to find out this information for your particular filter but my guess is that your pump is already close to max flow if not a little to much for that size UV. As long as your waterfall is not more than a foot or so in width when it enters the pond and it is matched up correctly for the filter you have I would say your 2100gph pump would work just fine. Here also is a past blog regarding pump selection that may help out as well as selecting tubing size. Good Luck and let us know if you have any other questions!

  2. I have a 1200 gal fish pond which I just added a large filter to last year It works very well but I still have green water.What size uv light could you recommend ? Is tis all that I need?

    • Hi Janie,

      Just to make sure, how many fish do you have in the pond and what size? Also, how often are you cleaning out the filter? Many times these few issues cause the majority of the problem. When sizing a UV you want one that will handle the flow rate of your pump. Any additional fitting or items will be dependant on the pump that you are trying to hook it up to.

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