What Is The Best Algae Remover For My Koi Pond?

Algae, the scum of the koi pond, can ruin a tranquil pond in days if left untreated. Whether it’s planktonic or filamentous algae turning your koi pond into a swamp, there are many ways to remove the algae with chemicals or naturally. Time to explore what is the best algae remover for your koi pond.

The best algae remover for koi ponds that works almost immediately is chemical algaecides, but it’s a reactive rather than preventive treatment. Barley straw is the best natural way to keep algae at bay, with regular maintenance, proper pond equipment, and pond planning.

Treating an algae-infested koi pond with highly-effective chemical products is one way of quickly getting rid of the algae. A safer and more efficient tactic would be to add certain elements, and maintenance, to the koi pond that prevents the algae from growing in the first place.

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What Is The Best Way To Remove Algae From A Koi Pond?

The best algae remover for koi ponds is algaecide products designed to keep the green monsters from growing further and kill them. These include some of the following products that we will discuss in detail:

With many algaecide products on the market, some more effective than others, it’s best to try the following peer-reviewed products. You don’t want to throw money in your mutant-friendly pond, with no relief from the algae, do you?

The following products have had mostly positive reviews (on average scoring more than four stars out of a possible 5) in thousands of reviews. What I do need to mention is that some pond owners were not happy with some of the products, the main criticisms being:

  • Fish dying after using the product
  • Plants dying after using the product
  • Algae were not removed or killed; in some cases, the algae appeared to grow even more.

I feel that you, as the consumers, need to know about the possible risk involved when using algaecide products, as most other websites do not mention some of the negative experiences that occurred to koi owners.

Some even promote products that specifically state that it’s not intended for use with ponds that contain koi.

The criticism received might have been due to the client’s negligence. It’s always better to be safe than sorry when it comes to our beloved koi fish, so please do proper research on the algaecide product before using it.

Always try to follow the manufacturer’s directions of use instructions on the product, and apply them diligently. Some products can only be applied to water with a certain pH level, so make sure to cover all the angles before use.

The best advice that I can give regarding algae and koi fish ponds is that you should be proactive in keeping algae from growing in the first place. I will explain how to do this later in the article.

First, we need to eliminate the algae before preventing it from taking hold in the pond again. When using any algaecide products, it’s vital to have a proper aeration system to prevent your fish from dying from oxygen deprivation.

Koi fish swimming in a koi pond with green water caused by algae

API Pond Algaefix Algae Control

API Pond Algaefix Algae Control is a one-gallon bottle containing polyethylene dichloride as its active ingredient and is EPA registered. The algaecide targets different types of algae:

  • String (Hair)
  • Blanket Weed
  • Green Water

Before applying this product, you must ensure that your pond has effective and active aeration. A fountain or aeration device is crucial for supplying the pond with oxygen to avoid losing any of your prized and loved koi.

When the algaecide starts working and the filter removes the algae, or when it settles on the pond’s ground, the oxygen levels may drop alarmingly, making aeration vital. This algaecide is especially effective when used in:

  • Koi Ponds
  • Fountains
  • Aquariums
  • Waterfalls
  • Water Gardens

API Algaefix seems to work best when used in smaller water bodies, as it works quite slow when dealing with larger algae-infected areas, up to 24 hours, depending on the water’s temperature.

Not only does it rid you of current algae infestations, but also against future outbreaks.

Click here for the price.

GreenClean Granular Algaecide

GreenClean Granular Algaecide contains 42.5 percent sodium carbonate Peroxyhydrate instead of harsher chemicals used in other algaecides like chlorine, phosphate, and copper. The product treats up to 16,000 gallons of water and begins working on contact, with results seen in one to two days.

GreenClean is EPA registered, and according to the manufacturers, it’s not harmful to any fish, koi included, or aquatic plants when following the manufacturer’s directions. For the most efficient results, apply the product in the morning hours or when the water is warm, as sunlight and warm water accelerates GreenClean’s granular activity.

Ensure to test the water’s pH level, between 6.8 – 7.8, before administering the granules. The water circulation needs to be turned off for 10-20 minutes, and you need to skim the dead algae from the surface to prevent future growth. Use the product at the first sign of algae growth for best results.

Click here for the price.

CrystalClear AlgaeOff String Algae Remover

CrystalClear AlgaeOff contains sodium percarbonate and Akali salt and effectively removes algae from a pond.

After applying the product, you need to skim any dead algae or organic material that floats to the water’s surface, ensuring that no dead organics float down to the bottom of the pond.

When most of your pond is covered, and the weather is hot or treating heavy growth – it’s best to apply to a ¼ of the pond only.

Wait for 14-days before re-applying again. This treatment method will lower the risk of your koi dying, and heavy growth may require a second treatment. Consecutive treatments should have a period of two days in between.

When the algae you need to remove is growing on a waterfall, do the following:

  • Turn off the waterfall pumps
  • Apply AlgaeOff to the affected areas
  • Let it sit on the waterfall for 20 minutes before turning the pumps back on.

Ensure that you follow the instructions regarding the correct amount to use for the size of your pond. Water temperature has zero effect on the application of CrystalClear AlgaeOff.

Click here for the price.

Microbe-Lift Algaway 5.4

Microbe-Lift Algaway 5.4 is an EPA-approved algaecide designed to remove many different algae types from water fountains and ponds. Again, if applying this product to ponds inhabited by glorious koi and plants, please make sure that a working aeration system is in place.

This algaecide also improves the quality of your pond’s water moving forward, and 1-gallon of this product can treat up to 45,424-gallons of pond water. The ingredients found in the algaecide are:

  • Poly Oxyethylene
  • Ethylene Dichloride

 Click here for the price. 

How Do I Stop Algae Forming In My Koi Pond?

An important part of pond maintenance is controlling algae growth; the simple truth – the fewer algae, the happier the koi fish.

Discolored water, poisoning, and asphyxiation are some of the side effects of this green disease. When there is an imbalance in a pond’s ecosystem, algae result from the imbalance, especially when there’s an overkill of nutrients in the pond.

Nutrients are caused by fish waste, decomposing plants, or debris. These nutrients act as fertilizer to the green plaque.

Types of algae that you may encounter in your koi pond (know thy enemy):

Prevention is much less effort than trying to cure algae. Here are some methods to stop algae in its slimy tracks without resorting to chemical algaecides:

Add Barley Straw

Who would’ve guessed that this cheap and natural straw would be the answer to controlling natural pond algae? It controls the pond algae, but it also removes it at a fraction of the cost of expensive – potentially deadly when used incorrectly- algaecides.

When barley straw decomposes, hydrogen peroxide (H202) is released, systematically killing the algae in the pond. Barley straw is available in the following forms:

Barley straw works best when placed near a waterfall, where water will flow through it. Make a little mesh basket, fill it with the barley, tie it closed with a piece of string, and attach the rest of the string to the waterfall so that the barley basket floats on top of the pond.

Using barley straw as an algae remover is not a quick fix, like applying chemicals to your pond, but rather a long-term algae prevention and control mechanism. It will take a few weeks before you start seeing the barley working, as it needs to begin decomposing first.

Physically Remove Algae

Get yourself some protective gloves and an old toilet scrubber, start scrubbing away the algae that you can reach, and you will see a visible difference immediately, as the pond filter does the rest.

Clean Your Pond Filter Daily

It doesn’t matter what type of pond filter you have; cleaning the filter every day will help remove algae much quicker.

Skipping a day or two will not be the end of the world, but getting into a maintenance routine regarding your koi pond will help to fight the good fight against the green enemy called algae.

If your pond doesn’t have a filtration system other than a waterfall, or fountain, investing in a good pond filter pump is a brilliant idea when you want to keep your pond clean without the added maintenance.

If you’re struggling with a pond with heavy fish loads, you will need a larger filtration system. Investing in a filtration system according to your koi pond’s needs is recommended, as implementing the correct system will also reduce the algae growth in your pond.

Ensure Maximum Aeration

Koi fish require a healthy dose of oxygen in their pond water. Having a waterfall or fountain installed is a good start, but it may not be enough for proper aeration, and using an aeration kit will be less expensive than pond pumps.

Treat Your Pond With Hydrogen Peroxide (H202)

We have discussed how barley straw releases hydrogen peroxide into the water when decomposing, but it takes a while before this happens naturally.

Leave the barley straw to do its work. However, if you want quicker results, treat your pond with hydrogen peroxide (H202).

Hydrogen peroxide will not kill your beloved koi fish or plants, be sure to research how much you can add according to your size pond.

Limit The Fish In Your Pond

A helpful reminder is small fish tend to grow, and big fish tend to populate. As your fishy friends start to grow and expand their family, the koi pond may become a little overcrowded.

The result is more fish waste and an environment that attracts the slimy green algae. A good practice is keeping the fish population in check – one to two koi fish for every 200 gallons of pond water.

Put Your Fish On A Quality Diet

Feeding your fish is an act of love; however, following a strict feeding regime is required. Only provide the koi quantities of food consumed within a few minutes. Anything extra goes and lies on the bottom, and too many results in larger amounts of fish waste.

Koi require a healthy diet, food that is rich in proteins, promoting growth, and which reduces fish waste, like some of the following:

Add More Aquatic Plants

As mentioned earlier, algae need nutrients to grow. Luckily for us, aquatic plants also require nutrients to survive. Increasing the plant life to 50% of your pond will immediately decrease the number of nutrients offered to the algae.

Another bonus when you add floating plants to your koi pond is that it will create shade for the koi, especially if your pond is in direct sunlight. When you find dead plants in your pond, remove them immediately, as dead plant matter will feed the algae.

Install UV Light Bulbs To Prevent Algae Growth

Installing UV Clarifiers is a must for ponds; pond water can turn green in a flash without it. Free-swimming algae particles are to blame for water turning green, and by installing a UV clarifier, their freestyle swimming days are over.

The emitted UV light destroys the green swimmers at a cellular level, breaking them down, where the pump filter springs into action and clears them from the pond. It’s a safe method to remove algae, won’t harm fish, and enhances the pond’s ecosystem.

Balance Your Pond Using Helpful Bacteria

A hugely beneficial natural pond treatment is to add some aerobic bacteria (good bacteria) to the water, which consumes excess nutrients converting them to gas. The following products will enhance your pond’s living conditions:


There’s nothing worse than algae attacking your koi pond. Watching your beloved koi space be turned into a green wasteland is no fun. Luckily, instant remedies like chemical algaecides are on the market to restore your pond to its former glory.

Then there are some more natural ways of keeping the algae at bay. Regular maintenance, and the right pond equipment, can also keep the algae from forming in the first place, negating the need to add chemicals to your pond.

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