How to Control Pond Algae

This article discusses the many factors involved in controlling algae growth in ponds. It is designed to better enable the pond keeper to have a full range of knowledge about combating algae growth.

Proper Equipment

Algae is one of the most talked about topics among new pond owners. Controlling algae is usually more of a problem for new ponds. A new pond does not have the proper balance of plants and animal life.

One of the most important things that you can do when setting up a new pond is to get the proper equipment installed. The pump you install should move at least 1/2 of the total pond volume for a water garden. The term “water garden” is assumed to be a pond with lots of plants and some fish. A koi pond usually has few plants and large fish requiring more filtration than a water garden. This type of pond is better off moving at least the full volume of the pond each hour. [Pond Volume Calculator]

Besides moving the water you also want to filter the water. The pump should move water through a filter that is sized for your pond. See How to Select a Filter for a page that provides choices for several pond sizes and filter combinations for you. Biological filtration takes several weeks or months to mature to the point that it makes a major improvement on your water quality. The filter needs to run 24 hours a day 7 days a week to work.

Proper Construction

Another major consideration for creating good water quality in the pond is one that is properly constructed. A pond should have about 40% of its surface area for the deep zone, which should be at least two feet for a water garden and three feet or more for a koi pond. Thirty percent should be an intermediate depth of 1-1/2 to 2 feet and the remaining 30% at least 1 to 1-1/2 feet deep. A slight slope to the deepest level allows for easier removal of debris from the pond [ See Illustration
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]. A pond skimmer is highly recommended as it can remove up to 85% of debris before it sinks. The pond should be constructed so that rainwater does not flow over the yard and into the pond. This is one of the more common causes of algae in the pond. Rain runoff carries with it lots of organic debris that contain nutrients that feed the algae. Also fertilizer or chemicals could be carried into the pond causing problems. If your pond is already constructed you cannot do much about the depths of the pond but you can alter the area around the pond to make sure that runoff does not flow into it.

A pond built using concrete, limestone, or marble will also tend to have a high pH, which can contribute to greater algae growth.

Proper Maintenance

Some debris buildup in the pond bottom is normal. As long as this sludge is no more than 1/4 inch or so physical removal is not necessary. In a properly constructed pond this debris ends up in a fairly small area where it can be removed when necessary. Course material like string algae and dead leaves can be removed with a net. A skimmer net or algae net does a good job of this. If the debris is too fine to be removed with a net then a pond vacuum works well. Using the following products should reduce the sludge and keep it to a minimum. The regular use of bacteria and enzyme products like EcoFix, PondZyme Plus, Microbe Lift line of products, GreenEx, or Simply Clear is not only good for the overall pond water quality they also help reduce odors, improve the health of the fish, reduces the amount of sludge in the pond, and reduces the algae.

Proper Plant Balance

If you have a water garden and not a koi pond then make sure you have the right types and numbers of plants in the pond. Anacharis or other underwater plants and floating plants remove excess nutrients from the pond by absorbing these nutrients for their own growth and starving the algae for its food source. Also provide approximately 2/3 surface coverage using water lilies, floaters (like Water Lettuce or Water Hyacinth), or other plants that shade the surface of the water. These plants reduce the amount of sunlight that penetrates the pond; this helps keep the water cooler and starves the algae for sunlight.
[Pond Surface Area Calculator]

Even though you have set up your pond using the right components, have added the proper type and number of plants, and do not have an excessive number of fish you could still have some algae. This is especially true when a pond is young. Other methods of algae control may be called for during the first few years of a pond. As a pond matures (as long as it hasn't been totally emptied and refilled) the algae gets less and less and may no longer be a problem.

Additional Algae Control Methods

What can we do while we are waiting for our ponds to mature? One thing that every pond owner should do is to add beneficial bacteria and enzyme products, as mentioned in the maintenance section above, to their pond on a regular basis. Not only is this good for the overall pond quality it reduces odors, improves the health of the fish, reduces the amount of sludge in the pond, and reduces the algae. If your problem is green water then you can solve this easily by installing an ultraviolet sterilizer. This is the only way to guarantee clear water 100% of the time [More information about UV sterilizers].

Filamentous algae have many algae cells attached together. It comes in many forms, it can be long and stringy, it can be short and furry or in the shape of webs or mats. The short velvet type of algae that covers the liner and everything else in the pond is beneficial. It helps provide a natural appearance to the pond. It uses nutrients from the water, provides oxygen during the day, and the fish nibble on it. This type of algae cannot be totally eliminated with fish and plants in the pond. String algae, which may coat the waterfall, is a little harder to control. You can physically remove it from the pond where possible. Filamentous type algae will flourish on waterfalls and in shallow streams because the sunlight is more intense providing more heat and light than what may be in other parts of the pond and there is a constant supply of nutrients flowing through it.

We carry other products that will control algae during the time that your pond is maturing. Algae Fix is probably the most effective. Barley Straw and Barley Straw extract are also effective for most ponds. Pond Dye shades the water, which limits the amount of sunlight feeding the algae. We carry blue and black dye, this is a cost-effective solution in large ponds and lakes, but it can be used in any pond. If your pond does not contain fish then Fountec is a great product to use. This product is safe for pets that may drink from the pond but not for fish. Or, in ponds without plants Pond Block is a good option.

Remember that fish and fish food add nutrients to the pond, which in turn feed algae. Don’t add more fish than your pond and filter will support and don’t overfeed your fish.

To Summarize:

1. Keep the organic load down by keeping runoff out of the pond and the sludge to a minimum. Vacuum sludge that has already accumulated. Less than 1/4 of an inch of sludge on the bottom should not be a problem.
   
2. Don't over feed or keep more fish than your pond will support.
   
3. Install a large biological filter and give it time to work, this could take several months.
   
4. Use enough, and the right type of, aquatic plants. This means surface plants for shade and floaters and underwater plants to remove excess nutrients.
   
5. Use biological treatments and give them time to work. Microbe-Lift will help but this is an ongoing process and takes time along with the methods outlined above for balancing your pond.
   
6. Use AlgaeFix to eliminate existing problems more quickly. Barley Straw Extract can be used in ponds less than 3000 gallons.
   
7. Install an ultraviolet sterilizer for the most effective control of singe-cell (green water) algae. [More information about UV sterilizers.]

Pond Shelf Depth Illustration

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