Common Pond Algae Treatments

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-Written by International Sales Manager, Joe Holz

Adding a Kasco Pond Aerator, Aerating Fountain, or Water Circulator will help add oxygen and surface agitation to your pond or body of water and will help with algae problems. However, aeration and water movement are not cure-all’s or silver bullets for algae or water quality problems. As with many things in life, it is all about balance and working with other items that produces the best results. There are several available methods for algae control and prevention, such as herbicides, bacteria and microbes, chemicals, UV sterilizers, and other additives like barley straw. Each has a slightly different way of attacking algae and some may work better in different situations and applications. However, each is designed to help eliminate and prevent algae from growing. Some only treat one generation of algae blooms, others may work for a longer period of time. Either way, when the algae dies off from natural causes or from one of the above treatment methods, there will be a large oxygen demand and Kasco Aeration can help. Also, the added water movement and mixing helps evenly distribute the treatments used and often makes the treatment work more effectively.

Physically Removing Algae

This method is used for filamentous algae and erect algae and is very labor intensive. This can be a very effective approach, however, as it not only removes the symptom which is the algae, but also the problem, which is the nutrients contained within that algae. You can use dip nets, rakes, seins, etc. to remove the material. When doing so, make sure to move it far enough away that it will not wash back into the pond on the next rainfall event.


Aluminum Sulphate (Alum) and forms of alum have been used to clear up muddy or cloudy water and remove phosphorus. It is not an algaecide or herbicide, but it binds phosphorus to starve the plants. The amount required is dependent on the phosphorus levels within your pond so it would be a good idea to get a phosphorus test kit and consult the label for application rates.


Copper is usually the first answer most people get when they bring up the subject of algae control. The most common form of commercially available copper is granular copper sulfate. Its effectiveness and cost as a broad spectrum controller of planktonic and filamentous algae has led to its high usage. Liquid chelated copper products are used to control a broad range of algae including planktonic, filamentous, and bottom attached types of algae. Consistent usage of some copper products can lead to bioaccumulation within the sediments and this approach is on the radar of some regulatory agencies, so a varied approach is probably the most sensible path to take. Copper is toxic to certain species of fish within the minnow family as well as salmonids depending on the dosage and water chemistry. Water with high hardness and alkalinity buffers copper from being toxic, but also limits its effectiveness. Check with a local lake manager for regulations and permits.


This product is a powerful herbicide/algaecide commonly used in natural ponds. It is safe to use according to the label for all types of algae control in natural ponds, but restrictions concerning fish harvest apply. This type of treatment works well with aeration to combat the negative effects of the algae die off. Check with a local lake manager for regulations and permits.


Granular based peroxides are super-fast acting contact algaecides for string algae. It is fast acting and bubbles as it oxidizes similar to medical grade hydrogen peroxide. The byproduct is oxygen and it is safe for fish at the recommended dosages. The remaining filaments and cellulose must be taken out of the water or it will settle back to the bottom of the pond. It is a bit more expensive than some of the other products, but is amazing for spot treatment and does not leave any harmful residues. Application rates vary greatly so it is important to follow the label instructions. As a side benefit, it works well at cleaning algae off of tanks, aerators, sidewalks, and even roofs. This type of control method works well in small applications such as watergardens. Check with a local lake manager for regulations and permits.


Dyes are often available in blue or black, powder or liquid, and act to shade water and reduce sunlight penetration that feeds algae growth. A side benefit that has been explored with some success is tinting the water blue or black to keep predacious birds from harvesting the fish in your pond because the birds cannot see the fish as easy. Aeration works great with dyes because it helps mix up the water and evenly distribute the dye that is added to the water. This method of treatment does not work well in ponds that are pumped from for purposes like irrigation or overflow into other ponds, because the dyes are removed during this process.

Bacteria and Enzymes

This non-chemical approach basically involves living organisms feeding off of the excess nutrients that would otherwise be available for plant growth. Typically they are a concentrated blend of naturally occurring bacteria and enzymes that rapidly biodegrade sludge, improve water quality, decrease suspended particulate matter and solids, and control odor if used correctly in the proper blend for the pond. Many different products boasting fantastic results are out there for consumers. What is critical to the success of using this approach are a few basic guidelines:

1. Bacteria are living organisms and if you use them in conjunction with herbicides there is a good chance they will prove to be marginally successful at best.
2. Dissolved oxygen levels must be at least 2 ppm for effective aerobic activity.
3. As the temperature drops, so does the effectiveness.
4. pH range of most products is 5.5 to 8.5.

Bacteria and enzymes will not kill algae, therefore, they are not labeled as an algaecide or herbicide. However, they have been shown to successfully outcompete algae for available nutrients. This is not an immediate fix, but can be an excellent, long-term approach to improved water quality.

Ultraviolet Sterilizers

This product basically works by using a wavelength of light that will zap planktonic algae. It is very effective for green water, but will do nothing for filamentous or erect algae forms because they will not pass through the unit to be exposed to the light. It should be viewed as a fairly effective approach for watergardens and fairly small ponds, but not that effective for larger ponds because of the costs associated with the larger scale units and applications. Flow rates are readily available from any of the major manufacturers of this type of equipment and are measured by micro watts per second per centimeter squared.

Barley Straw

Barley straw has been used as a natural alternative to algaecides for centuries throughout England and Scotland. If it is to be sold as an algaecide here in the US, it must have an EPA registration number. Research has suggested that barley straw can aid in balancing the water quality by lowering the pH and carbonate hardness of the water, which can control the growth rate of certain undesirable plants and algae. As the straw degrades in the presence of water and sunlight, it creates peroxide, which can kill both filamentous and planktonic algae. It is better at deterring algae than controlling it once there is already a problem. Application rates are all over the board and success varies from pond to pond. A commonly recommended dosage for private ponds (this is how many get around the EPA registration problem) is 225 pounds of barley straw per acre of water (about 5 bales) in relatively shallow ponds of 4-5 feet deep. It is critical that the barley is loosely packed and that it gets some type of water circulation through the bales. Kasco aeration and circulation products can add this water movement and circulation needed for better success. The bales can also act as a substrate for beneficial bacteria to adhere to and grow. There are also several products, such as barley straw pellets and barley straw extract that can be added to your pond instead of the actually bales, but these products are more expensive.

Ultrasonic Sound Waves

The basic science behind these units is fairly sound. They use resonance of ultrasonic waves to kill algae. A submersed transducer generates ultrasonic waves that shock the algae and kill the algae by tearing the gas vacuole which allows them to float. This type of product should not harm your fish. The problem with this approach is that the cost for the unit is high and the results are highly variable and can be marginally successful at best. Each pond should be looked at almost as a separate organism with varying water quality. A unit should then be sized for those conditions. Another major issue is when some strains of algae are killed, others will take over to feed on the nutrients. These other species of algae may not be affected by the ultrasonic machine and the end result is still a green pond.


There are several types of skimmers available on the market. Skimmers are usually not as effective in larger ponds or lakes, but work well in small applications such as watergardens. There are several manufacturers on the market that make skimmers as part of their pond kits that include filters, liners, pumps, etc. to create a watergarden. The skimmer collects water and floating plants and sends them through the attached filter. The filter takes out the plant material and returns the clean water. Larger scale skimmers have grown in popularity and can be an effective way to address some larger ponds. Continual monitoring and possible removal of material is critical.

  • Laurie

    I have had success with filtration, but do see how using some of the things you suggest may help. Great tips, thanks for sharing!

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