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How To Get Rid Of Pond Algae Without Killing Fish

Posted by on Jan 09 2024

Getting rid of pond algae is a task that many pond owners face. Although a small amount of algae can be beneficial to your pond’s ecosystem, excessive algae growth is not welcome. 


Not only is it unsightly but too much algae can smell bad, deplete oxygen levels and unbalance the water quality of the pond, which can negatively affect the health of your fish and other pond dwellers. Since pond algae removal is an essential part of pond maintenance,  you may be wondering how to get rid of pond algae without hurting your fish. To help you remove and reduce pond algae, we’ve compiled some tips to keep your pond clear and your fish safe and happy. 


Identifying Types of Pond Algae

When it comes to clearing pond algae, knowing about the types of algae you have in your pond can help you get rid of it and reduce its growth in the future. Algae in a pond can look like a layer of green sludge floating on the surface, thin green strands that cling to plants, rocks and the pond liner or a general greenish discolouration of the pond water. The main types of algae that can affect your pond include:


  • Green algae - sometimes referred to as “green water” or Blanketweed, green algae can be caused by excessive fish waste.

  • Cyanobacteria - also known as blue-green algae, this type can be caused by stagnant water.

  • Filamentous algae -  sometimes called “string algae”, these hair-like strands can be caused by increased levels of phosphorus and nitrogen in the water.


What Causes Algae Overgrowth?

Although the presence of algae is a naturally occurring phenomenon, several factors can contribute to excessive algae growth and negatively impact your pond’s ecosystem. Here are a few of the factors that can trigger algae overgrowth.


Excessive Sunlight 

Like all plants, sunlight triggers photosynthesis and too much sun can cause algae to thrive. If your pond has no shade and no surface-dwelling plants to block the sunlight, this can cause algae blooms.


Excessive Nutrient Levels

When nutrients like phosphorus and nitrogen are excessively present in your pond, this can start a process called eutrophication which influences the abundant growth of algae. The algae feed on the nutrients just as any other plant would so maintaining excessive levels of phosphorus and nitrogen in the pond water can increase the presence of algae.


Poor Water Circulation

When your pond has insufficient water circulation, this causes the oxygen levels to decrease and bacteria to increase, which can harm your fish population and affect the chemical balances and the overall water quality.  Algae also thrives in stagnant water so ensuring you have an appropriately sized pond air pump can help to circulate the pond water. Adding air stones to the pond can also help to increase the movement and oxygen levels in the pond.


Inadequate Filtration

If your pond lacks proper filtration, this can lead to a build-up of organic debris in the water like uneaten fish food, fish waste and other pollutants. This waste can lead to nutrient imbalances in the water which will fuel the growth of algae. 


How do I Clear my Pond Water Without Killing Fish?

One of the nicest things about having a garden pond is having the opportunity to have a thriving fish community. But when you have fish, knowing how to get rid of algae in a pond without harming them is essential. Luckily, we’ve got some pond algae removal techniques that won’t hurt your fishy friends.

Fish-Friendly Tips for Removing Algae From a Pond

  • Use pond skimmers and pond nets to physically remove pond scum and algae sludge from the surface of the water.

  • Pond vacuums are a great way to remove algae that has accumulated at the bottom of the pond. You can use the various attachments to get into hard-to-reach areas and you won’t need to worry about the fish as they’ll instinctively stay away from the vacuum.

  • Choose the right pond filter and filter media. As well as removing impurities from the pond, a good filter will trap the algae as it passes through resulting in cleaner, clearer water for your fish population.

  • Invest in pond treatments like fish-safe algaecides, natural enzymes and fish-friendly beneficial bacteria to promote the growth of good bacteria in the pond. The bacteria helps to strip the nutrients that the algae feed on from the pond, effectively starving them. This good bacteria helps to maintain good water quality as well as get rid of pond algae.

  • Using Barley Straw is another way to get rid of pond algae without harming fish. Place the Barley Straw on the surface of the pond and leave it to break down. As the straw starts to decompose, it releases hydrogen peroxide into the water inhibiting the growth of algae. Barley Straw extract is a great, fast-acting alternative that comes in liquid form and works on contact.


Fish-Safe Tips for Controlling Algae in a Pond    

Now you know how to get rid of pond algae without causing harm to your fish, here are some ways to control algae growth and prevent build-ups in the future.


Invest in Algae Eating Fish

Choosing fish that eat algae can help to reduce algal blooms. Avoid overcrowding your pond as the increased waste production can contribute to increased algae growth. Some popular algae eaters include:

  • Koi fish

  • Pond Loach

  • Common Pleco

  • Goldfish

  • Siamese Algae eaters ( these will need to be transferred indoors during winter)

In addition to fish, some snails are voracious algae eaters and species like ramshorn snails will feed on algae as well as rotting plant debris.


Add Beneficial Pond Plants

Increasing the amount of oxygenating plants in your pond will benefit the overall quality of the water. As your fish naturally produce waste that turns into nutrients, pond plants will absorb those nutrients, leaving little for the algae to feed on. This can help to slow down and control the growth of algae. Some beneficial aquatic plants include:

  • Floating pond plants like water lilies and lotus will help to block excessive direct sunlight and inhibit algae growth.

  • Submerged plants like hornwort are known as oxygenators and release a constant stream of oxygen while absorbing excess nutrients.


It is recommended to place 2-3 submerged plants per square metre depending on the size. 1-2 plants per square metre of pond space is appropriate if you have larger plant bunches.


Avoid Overfeeding Pond Fish

Be sure to maintain responsible feeding practices as this will play a pivotal role in keeping the pond ecosystem balanced by reducing the risk of algae blooms. Overfeeding can result in uneaten food decomposing the water which acts as a catalyst for uncontrolled algae growth. By regulating the amount of fish food provided and promptly removing any portions of uneaten food, you can reduce the nutrient buildup which will create a healthier pond environment where the likelihood of algae-related issues is reduced.


Regular Water Testing And Pond Maintenance

The nutrients in pond water provide food for the algae so ensuring the levels are just right will help to prevent nutrient overload and excessive algae. Regular pond maintenance and water testing are the best ways to stay on top of algae growth. Using pond test kits to monitor nutrient levels and consistent removal of debris should become essential components of your maintenance routine. This frequent practice will help to prevent the accumulation of excess nutrients that fuel algae growth. 



By implementing strategies like proper nutrient management, enhancing water circulation, and maintaining a balanced ecosystem, you can contribute to a healthier pond environment and allow your fish and pond wildlife to thrive. CD Aquatics supplies a range of fish-friendly products to help get rid of algae in your pond. Browse our range of pond supplies from filters to barley straw to water testing kits or contact us with any pond-related questions on 01922 416284.

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