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Clearing Algae from a Pond with a UV Light

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Want a clear pond? This UV light setup helps clear green water.

How to clear algae from a pond with a UV light. Instructions on how to install the ultraviolet light.

This post may contain affiliate links. Using these links helps support my blog. We are not plumbers or pond installers, just some folks who read the instructions and looked up information online. Please make sure to do your own research and take safety precautions. Thank you! 

We recently had a pond installed for our front yard. With a large filter, plenty of plants, and only a few fish, it was clear until about four thousand frogs moved in. At that point, however, algae started setting in and the pond water wasn’t as clear. We wanted to clear it up and we were told that a UV light might solve the problem. Note that UV lights help clear up algae, but don’t improve water quality so if there’s an issue with the balance in your pond, you’ll still need to address that problem in other ways.

Here’s a “before” photo of the pond. It wasn’t terrible, but quite green. This is after a very short amount of time after install so you can imagine that it would have gotten worse over time.

Algae in a newly established pond.

Supplies Supplies listed below may include affiliate links to the products.

  • UV Light Sterilizer (there are other options, this is just the one we used)
  • Hack saw (or something else to cut the ends if needed)
  • Hose clamps
  • Good scissors
  • To already have a filter/pump installed. This covers how we installed ours and we have a fountain. I’m sure you’ll need to adjust this a bit if you don’t have a fountain. 


Just to explain what this light does, it connects through the plumbing in your pond and the water cycles through the closed tube for the UV light (the bulb itself is protected from the water). The UV lights kill the algae, returning clear water to the pond.

Initially we weren’t clear on how this was installed. I thought it would be submersible, but it IS NOT SUBMERSIBLE. This means that it doesn’t hog space in the pond though so that’s fine.

We started install by finding our plumbing for the pond. The tubing we pulled up is right behind our waterfall. (Excuse the dog bone, haha) This means that the water goes through the UV light AFTER the water goes through our filter, which is on the other side.  The pump from the filter to the fountain helps push the water through the UV light, then back into the fountain.

Ideally you want this placed after the filter so debris doesn’t get stuck inside your light. 

Original plumbing for pond that brings water from filter to fountain.

We turned everything off- the electricity and plumbing- in the pond for safety (and to keep us from getting hit with a lot of water when we cut the tube).  Then we cut the tubing in half.

Cutting the tubing for the pond filter to fountain so we can install a UV light.

This cone like piece needs to be cut down to the size of your tube (the black tube). Don’t cut it too big.

Nose adapter cut to size.

Insert the hose adapter (clear piece) into the hose. Make sure it’s in very snug. We used a mallet to hammer it in because it was so hard to get in. You’ll do this on both sides of the hose. 

Fitting all of the pieces together for installing a UV pond light.

Tighten the hose clamp around the tube.

Tighten hose clamp around the tubing.

Once you have all of the pieces attached, you can screw each end into the UV light. Turn on the pump for the filter to see if you have any leaking. If you do, turn everything off so you can adjust your attachments. You don’t want water leaking from this.

Attach your tubing to the UV light, making sure you have a good seal.

Once you have a good attachment and no leaking, you’re ready to go. You can hide this under a fake rock or just leave it be. You will need to plug in the light of course. Make sure to clean and store this for the winter months.

It’s hard to take photos that really show how much clearer the water is due to the bubbles from the fountain, but we can now see the plants at the bottom which is just amazing! The paperwork says it takes 3-5 days to see the results, but it probably depends on how much water you need to cycle through. Our pond cleared up pretty quickly, although it got better over a few days.

Clear water a week after installing the UV light in a garden pond.
Water clarity and decreased algae after a week using a UV light in the pond.

Come back NEXT WEEK to see the complete pond setup! I’m so excited to show you our pond and patio setup, as well as our huge privacy planters. These posts will go out over the next two weeks so make sure to subscribe so you won’t miss them! I also have a couple posts in the works about ticks and tick prevention (because I know many of us love the outdoors, but may not love Lyme).

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And don’t forget to check out last week’s post on our garden and path install. This garden is absolutely stunning now and it helps improve drainage and reduce mud in the path to our backyard.

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How to clear algae from a pond with a UV light..

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Thanks for Reading! -DIYDanielle

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