How To Get Rid Of Algae In A Koi Pond?

You finally got that beautiful, relaxing koi pond built. To keep it looking that way you will need to maintain it. Algae is one of the problems you will have to tackle.

So do you know how to get rid of algae in a koi pond? Plan and build your pond in a well-shaded area. Put your pond where it is covered in about 65-70% shade. Purchase a pond skimmer. Have plentiful plants around like pond lilies. Use a net or pond brush on your pond regularly. Use pond dye in your water to dilute the amount of sunlight

How To Get Rid Of Algae In A Koi Pond_

You Need To Know How To Get Rid Of Algae In A Koi Pond So This Frog Lives On

Every Spring pond owners all have to deal with algal blooms flourishing. This is because of the warmer temperatures, sunlight, and plentiful nutrients from dead plant matter and fish waste fuel the algae growth.  You need to have some idea about what kills algae in order to eradicate it? As you see above, this isn’t nearly as complicated as you probably think it is as I like to keep things simple.

Things That Inhibit Algae Growth

There are many ways to keep that algal blossom from blossoming

  • Shade-When you decide to build your pond find a shady spot. Like I mentioned above, direct sunlight is what gets algae growing out of control.
  • Special Algae Brushes-There is special brushes you can use to skim across your pond to collect all the algae and other debris. Brushes like the Pond H2O Pool Brush can be swiped across your pond to collect the algae on it.
  • Algaecide-Places sell algae killer for your pond. Some are for pool use and I’m not sure if the ones for a pool are safe for a pond filled with expensive fish. So find one for pond use. AquaShade Organic Plant Growth Control is a good product to use.
  • Koi- Your Koi love to eat algae too. They eat all plant life around them and a lot of bugs. They are little hogs.
  • Nets- You can also use a net over a brush if you want. It will do the same job. Just don’t scoop up your fish as I imagine they probably don’t like it.
  • Check Your Ponds pH Level- When you lower the ph in a koi pond you are at least allowing the live good string algae without killing it and allowing the dead algae matter to float around wreaking havoc.

In Spring And Summer, You Can Guarantee Algae Will Happen

Algae like that sunlight stuff. Like plants, algae need sunlight to convert the carbon dioxide in the air into organic compounds, especially sugars. And when is the sunlight the brightest and most abundant? You guessed it. Summer

That is why your pond gets green or brown looking during this hot time of the year. It’s doing your fish a huge favor though when it’s alive. It provides much-needed oxygen to your marine friends. Your koi also eat algae as a food source too.

So it serves many positives purposes, but you got that Koi pond built to see your fish and that algae are very effectively preventing that. A murky, gross mess is what you see.

Who Wants Pond Algae?

Once algae die it depletes the amount of dissolved oxygen in the water which could be helping your fish thrive. String algae contribute to producing more oxygen and build up oxygen bubbles that get caught in it’s “hair”. So string algae aren’t all bad besides taking up your whole pond making it unsightly. Anything that improves oxygen growth can be good news for koi.

Unfortunately, this same string algae that were semi-healthy for your fish in this form will soon die and whither sinking to the bottom. It then gets broken down by bacteria using that same oxygen to do so. So living string oxygen promotes more dissolved oxygen. Dead string algae take away the oxygen in the water.

A Koi pond owner sure doesn’t want it. You want to be able to sit on your patio, relax and watch your Koi swim around happily. That pesky algae bloom makes it impossible to do that. It sure doesn’t take long to take over either. Like overnight it seems.

It starts to use up a lot of oxygen once it dies and rots. Your pet fish need that oxygen to thrive. So you need to manage it as best as you can.

Why Does Algae Grow In The Winter And How?

I actually wouldn’t mind seeing algae in the winter as I ain’t going outside anyway in that cold air. Not if I can help it anyway. Why doesn’t algae show up in the Wintertime instead of the inconvenient Summer?

Algae do grow in the winter, but it doesn’t overtake things as it does in the summer. You don’t have to worry about it as much. I would prefer it to be around in the Winter more so I could enjoy the crystal clear water and my Koi Carp swimming around happily. The Koi won’t eat in the Winter because of a slowing in their metabolism which means Winter does not provide the best temperature for Koi to gorge on algae blooms.

Some traits of Winter weather on a pond are more advantageous for pond algae. Algae feed on byproducts of decomposing organic matter and debris. In warmer weather, bacteria consume these byproducts and algae doesn’t get as much of it.

As it gets colder, however, the bacteria become dormant. That leaves a decomposing-byproduct-all-you-can-eat buffet for the Winter algae to consume. The combination of a little light and all that decomposing matter the algae have all they need to thrive.


What Can You Do?

You can do what you can to limit the sunlight that algae has access too by putting pond dye in your Koi pond. This dye also gives your water an attractive bluish hue. Without light, the algae can not go through Photosynthesis so it can’t grow.

Have a pond skimmer installed. Pond skimmers are mechanical filters that feature some way to catch debris as water flows through it. Including algae.

Keep your pond pump pumping. Keep the water moving so it doesn’t become still and stagnant. Algae love stagnant water full of all kinds of dead matter to feast on. The pond pump also keeps oxygen circulation for your koi fish.

Now Your Ready To Conquer Algae Overgrowth

Following these tips will keep your pond from being overtaken by algae running amuck. Pond pumps, pond dyes, and skimmers are all really helpful when it comes to tackling your algae problem. Don’t use chemicals if you have fish in your pond. No pool algaecide or anything else that may contain ingredients that could be harmful to your fish.

Also, keep in mind the benefits that algae provides for your pond, fish, and ecosystem as well. During the photosynthesis process, the resulting oxygen can be saturated into the water for your Koi giving them breathing room. Koi, like any other fish, have to have their oxygen from the water and not the air.

Plan to build your pond in a shaded area to keep it out of the sun. Preferably you would have a building or some structure providing most of the shade instead of only trees. I say that because you don’t want a lot of leaves and debris falling in your pond and just rotting. Strive to have at least 70% of your water in shade. Your koi will have it made in the shade.

Are algae beneficial in any way? Algae when it is still alive definitely has its benefits. The oxygen that it supplies in the water alone is a great help to giving your koi some air. It’s also a food source to your koi in the summer. Planktonic algae, for example, make up the first link of the food chain for other organisms that are food to the fish.

What chemicals can you use on a koi pond? The chemicals you use in your pool sometimes don’t translate over well to using in a koi pond. TetraPond Algae Control is a good choice. Nualgi Ponds is another popular one that is safe. Anything chlorinated should NOT be used. Most pool products contain chlorine which is bad for fish. Pond dyes are another thing used to inhibit sunlight which algae blossoms need to live and an added benefit is the awesome blue hue it gives your water.

Are green algae plants? Algae are not considered plants because they are just aquatic. They can’t survive on land.

Can algae harm fish? That depends on the type of algae. Just like plants, some algae are toxic. A small number of algae types are poisonous and can cause harm but not many. Even with the harmful ones many just have negative effects. Consider the fact that plants, for the most part, are really healthy for us. Poison ivy, however,  will make most people itch and have a rash. A few algae here and there generally have terrific health benefits just like described above. It’s just when it starts to overtake everything where it becomes a problem.



Do you have a method for killing off algae growth? Let me know in a comment if you have a cool way of keeping your pond algae-free. Thanks for visiting.

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Image by Marc Pascual from Pixabay

16 thoughts on “How To Get Rid Of Algae In A Koi Pond?”

  1. Nice article and nice website. I appreciate your bulleted and formatted list. It helps the article be easy to understand and follow.
    The pond dye sounds like a great idea. I never would have thought of that but it is very smart because it just darkens the water and reduces the sunlight that gets through. Is it okay for the fish? If so, I can’t think of a better way to control algae in your pond. It seems like there is a difficulty in picking a method of algae control, since you don’t want something so strong that kills your fish but you do want to keep the algae down.
    Using the brushes and Nets also sounds effective but relatively non-intrusive. Thanks for the recommendations I will forward this to anyone who may be interested.

    • The pond dye is safe for fish. If you think about it it has to be. Most people who have ponds have fish in them. Would a pond-dye-making company stay in business with a product that could potentially harm fish? The pond dye is as good as the other methods discussed above. I also like having a nice looking blue pond. Thanks for the visit.

  2. My brother is about to start a pond and Koi is one of his choices to breed. I appreciate the info that you shared, that there are some algae that are actually harmful so the best thing to do is, get rid of them like using a dye. It seems the dye you have mentioned is okay and safe, but for idealists like my brother, what do you suggest he use as a natural alternative to the dye commonly used in this process?

    • Hey there Gomer. The other ways work too such as getting a net and scooping that algae up in it. A lot of koi owners don’t want to use dyes or other chemicals so they make sure their filters are running and finding ways to scooping out the mucky algae deposits. I hope this answered your question. Thanks for visiting.

  3. Wow! This is such an informative article on getting rid of algae in a koi pond. Though I do not rare fish neither do I own a and but I have an uncle who owns ponds and that is his major occupation and he has been complaining about the invasion of algae on all his ponds so, I will suggest this post to him and hopefully, this would work out for him and help him in getting rid of algae. Thanks

    • Hey RoDarrick. Algae is a big complaint from pond owners and I hope this post helps your uncle out. I also mention that some algae in a koi pond is a good thing as long as it’s is alive. Too much will just overtake your pond and make it look swampy. Best of luck to your uncle.

  4. This is a great post. The way you have outlined it makes it easy for me to understand it concisely. I have been looking to start my own koi pond and I needed to know what to expect. It’s good to know that although algae is good for the fish by giving them oxygen and food sometimes, it can also the taken away when not needed. I didn’t know about the  pond dye either. I have learnt a great deal from your post. Thanks alot.

    • I hope you start it soon. Now you know how to get rid of algae in a koi pond when you encounter that specific problem. I’m glad it was helpful. Thanks for visiting

  5. Hello Randall. This is great information. I think having a koi pond could be a lot of work but some of my friends have them so it must be worth it. I do a lot of travelling so unfortunately this isn’t something I can do but I will be sure and pass this on to my tnem. You have provided enough information on the dreaded algae and I am sure they will appreciate it. 

  6. Thank you for the information. A while ago, my uncle has started to build Koi pond in his garden. I and he are a noob in this area, but we already heard about the potential Algae problem for the pond. Between the dye and and skimmer, which one do you recommend more? We have a rather limited budget, so it may come into our consideration. Thanks in advance for your answer.

    • Hi there

      The skimmer is probably more necessary when starting out. Pond dye is an additional bit of algae killing protection that also adds in a nice blueish hue to your pond for more visual appeal. Thanks for reading.


  7. Hi, Randall!  What a great post for those who are raising koi!  Algae is inevitable, no?  I like how you have listed everything out in a clear and easy-to-read manner.  The information you have listed will help anyone with koi succeed in keeping algae at bay.  Thanks for the informative article.  It’s obvious you’ve done extensive research!  

    • Hello there!

      I appreciate your visit. Algae is one of the big problems pond owners face so it is a subject that’s definitely needs to be covered. I hope you come visit my site again soon. Thanks.

  8. Hi, Randle.  I enjoyed reading your post.  Great information.

    I have thought, over the years, that it would be nice to have a Koi pond in my back yard but never actually had the opportunity to do so.  Now I am retired and I live in a co-op so I don’t think it’s possible anymore.  But, it’s nice to dream.

    They are actually very nice to look at and watch as the fish swim around. It.s kind of calming.  Takes your mind off the busyness of the day.  Some are also quite beautiful as well.

    The only drawback I can see to have a pond is the potential for nighttime thieves.  You know, the black furry ones with the mask?  Any suggestions on how to keep them out of a Koi pond?  Some of those Koi can get pretty big and cost a lot to replace so some kind of protection would be good I think.

    Maybe some sort of security for those other poachers might be a good idea as well.

    I may not have a Koi pond but it’s always nice to learn something new from time to time.  Thanks,


    • Hi Wayne

      Security around your pond is something you need. I haven’t got around to covering that subject on my blog yet, but it sounds like it’s time to cover it.

      There are nets that you can put over your pond to keep stray animals out. You should also go onto Amazon and search “pond scarecrow.” Those things are COOL! People have been inventing ways to repel the rodents ever since keeping koi was a thing. Some security cameras have strobe lights that can be activated that scare away unwanted guests too.

      Raccoons aren’t the only predator to watch out for. Herrings, a large bird of prey, are also menaces that can steal your fish. You have to protect your fish from grounded animals and flying animals too.


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