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How to Prevent, Treat and Control Pond Algae

How to Prevent, Treat and Control Pond Algae

Algae, the unsightly green stuff that grows in our ponds from time to time. It's one of the most common issues pond owners face.

All ponds will eventually come across this issue. We can help you keep it at bay, but first, we need to understand it.

In Canada, we have 2 main types of algae that form, Green Water Algae (suspended algae) and String Algae. We'll be focusing on these two types. If you haven't already, you'll want to learn what these two algae's are and what causes them. This important knowledge will help you beat your algae issues and keep them away.

To learn more about what pond algae is and what causes it, click HERE

We'll be going over how you can prevent algae before it forms as well as how to control it and get rid of it once it does form. Algae can be an annoying sight that goes away after some time or a continuous issue, following these steps will help rid your pond of it faster and help keep it away.

Control and Prevention for Both Types of Algae

Control and prevention is the best thing you can do for a pond. Once algae starts forming you can still get rid of it fairly easy; however, once its a major issue, it can take great lengths and effort to get rid of it. The best method is prevention.

Both Algae forms are relatively similar so we'll start with some things you can do to control and prevent both of them. If you already have algae issues, you should review the prevention section as well and take the appropriate measures and treatments available.

Since the two main factors to algae growth are 1. Excess nutrients and 2. Direct Sunlight, we'll want to control these issues no matter where we are in the prevention or control timeline.


Limit the Amount of Fish in Your Pond

Pond fish such as Koi and Goldfish, tend to be larger than aquarium fish, as such we don't follow the same rules as we would an aquarium. A pond should have no more than 1 inch of fish per 10 gallons of water.

Let's say you have a pond that holds 1000 gallons of water, you would want no more than 100 inches of fish. This could mean only 3-4 Koi or 5-7 Goldfish if they are fully grown. Koi grow 24 - 36 inches and Goldfish can grow up to 15 inches fully grown.

Control Fish Feeding

Fish food breaks down quickly, causing water imbalances. As such, we need to ensure we are only feeding fish the amount they need. To solve this issue, there are fish foods that don't break down the same as others or cause cloudy water. These foods can help. Also make sure you follow the feeding instructions and don't overfeed fish. A general rule of thumb is to feed the fish only what they can eat in 4-5 minutes, then remove the rest of the uneaten food with a net.

Add Some Shade

Since direct sunlight is a cause of algae, we can try minimize this issue or remove it completely. Adding a large tree around the pond to help block some sunlight is one way to reduce direct sunlight on the pond, just ensure any falling leaves are removed from the pond before they decay.

Another shade option is water cover plants such as lilies or lotus'. These plants cover the surface of the water which limits the sunlight's penetration into the water. In turn this reduces the risk of algae. We recommend up to 2/3 of the pond covered in pond plants.

Add Aquatic Plants

Aquatic plants used to help prevent algae

Aquatic plants are a great way to remove excess nutrients in your pond. The plants consume the nutrients and clean the water. You'll want to make sure the plant roots are either planted directly into the pond substrate or into pond planting media. They should not be planted in a typical potting soil as there are too many nutrients that will cause further issues.

Control What Goes in Your Pond

Controlling what goes into your pond is a great way to reduce the risk of algae and also help get rid of it if it does form.

Things to look out for and remove or deter:

  • Animals urinating - Causes water imbalances. Dogs, deer, etc.

  • Frog, turtle and fish waste - Too many fish, reptiles or amphibians in the pond

  • Bird waste - Fecal matter in the water causes issues, geese are a major issue around here

  • Leaves and debris - Remove with net asap so they don't decay

  • Fertilizer and lawn runoff - Added nutrients cause water imbalances

  • Soil leaching into pond - Ensure there is no exterior soil leaching into the pond after a rainfall or storm, the nutrients can cause issues

  • Rainfall - Rain brings added nutrients into the pond which is why often times a heavy rainfall will cause water quality issues

  • Blown in dirt and debris - If you live near a soil distributor, farm with machines constantly working the field, etc. Blown in soil can be causing water quality issues.

If you're constantly fighting off rodents, birds and animals from your pond, it may be worth looking at a deterrent such as a sprayer or crocodile decoy

Did You Know? - Lightning Can Cause Algae! When lightning strikes, it tears the bond in airborne nitrogen molecules. These atoms then combine with oxygen molecules to form nitrates. These nitrates are carried by rainfalls, which is why your grass is greener after a storm.. Or your pond has water quality issues / algae after a storm... Nature!


There are some solutions that will help get rid of both types of algae, these can be helpful tools to keep algae away and prevent it.

Water Treatments

Beneficial Bacteria - A healthy system helps fight off water quality issues. Beneficial bacteria's are essentially probiotics for ponds. These bacteria's will compete against algae for nutrients which in turn will reduce algae growth

Aeration units oxygenate the water which helps keep the bacteria's alive. This in turn will help keep the bacteria's healthy so they do their job more effectively and utilize the nutrients which limits the algae from access to nutrients.

A pond, dyed to help control algae

Pond Dye - Pond dye will help reflect the sunlight by turning the water a different colour.

The sun doesn't penetrate the water as easily which in turn will reduce algae. Although some don't like the look of pond dye, it can be a useful tool to reduce and control algae.

1. String Algae Specific Prevention and Control

String Algae Control and Prevention
String Algae Example - Resembles hair strands

If caught on time, string algae can be extremely easy to remove and prevent. By using the following methods you may rarely see string algae, if ever. The IonGen works like magic at preventing and eliminating string algae, we install them in almost all of our pond builds.

Remove it By Hand

If string algae is forming in your pond, the quickest way to help clean it up is to get your hands dirty, scoop it up with a net or some type a rake and remove it from the pond. Although this wont stop the cause, it will help clear things up quicker and make your pond look a lot better in the process while slowing growth. Be sure to remove it quickly as it will grow and multiply. Be careful while removing it as algae spores can be released into the water during the removal process.


A product such as EcoBlast Granular Algaecide is a great way to remove it quickly and spot treat affected areas. Its easy to apply and can be used at any water temperature. Some algaecides are not available in Canada so you may have to do some research to find one.

This unit can be installed directly into your pond plumbing, it requires continuous water flow through the probe. This easy to use system is extremely effective in killing string algae. If algae starts forming you simply push a button, the algae magically disappears over the course of a couple weeks and you drop it back down at the push of a button. It kills algae using copper ions. The unit is fish, plant and animal safe. Just make sure you follow the directions for use as prolonged high dosing can harm fish and plants if misused. If the water quality issues aren't resolved at the same time, the algae may come back.

2. Green Water Algae Specific Prevention and Control

Green Water Suspended Algae Pond Issue
Green Water - Suspended Algae - a.k.a. Green Pea Soup Algae. Yikes! We did a pond cleanout and helped it get back on track!

If you're experiencing green water (suspended) algae in the spring, chances are it will clear up in 2-3 weeks as this is a common issue that arises with changing temperatures and while the beneficial bacteria's are colonizing in the rocks and filters.

The warmer temperatures also awaken plant life which will help utilize the excess nutrients.

If this problem does not solve itself within a few weeks or gets severe, it will be time to start taking the extra steps.

Shade The Pond

We're adding this again as sunlight plays a major role in the growth of suspended algae. Using covering plants, dye or trees to block the sun rays will help you fight off suspended algae.


Using an algaecide to kill the existing suspended algae is a great way to quickly clear up your pond. This is not a prevention method, it is a treatment that only needs to be used when algae forms. As mentioned above, most algaecides are not readily available in Canada and will require some research to find it.

UV Filter / Clarifier

Filters with a built in Ultra Violet bulb (UVC bulb) will help eliminate suspended algae as it passes the bulb. This is often times an effective method to prevent and eliminate suspended algae.

Providing adequate filtration and filter media for the beneficial bacteria's to colonize is a great way to keep your system and bacteria's healthy. As mentioned, having a strong bacteria colony will help keep the nutrients away from the algae.


Using these methods will help prevent and control algae issues. The best method is prevention; however, if you catch the issue quick enough, you shouldn't have a hard time fixing your algae issue.

If you're in Canada, we retail pond products to help with any issues or help with your pond construction. Visit:

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Q: What method worked the best for you while getting rid of your algae issues? | Comment Below

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