ALGAE – It Is All About Balance

Algae are a normal part of any organic pond ecosystem. The main goal of having a “clean” pond is having a balanced pond ecosystem, instead of having a pond without algae.
Nothing is more frustrating than battling algae in a pond. Green water and string algae can be a big problem. There are many factors that contribute to excessive algae growth. Fighting and preventing it can sometimes seem like a losing battle. However, prevention and control of algae is much easier than you probably think.


Two Types of Algae


There are two main types of algae that develop in ponds. The first type is suspended algae.  Suspended algae creates green water. The second type is filamentous algae which is also known as string algae. It forms in hair-like masses.  It attaches itself to rocks, plants, or other available surfaces in the pond. Although both forms of algae can be a real nuisance, they are two different types of algae.  It helps to understand the causes for each.

Suspended algae growth usually occurs in the spring when the pond is first waking up and the water temperatures are still low. As temperatures begin to rise, and plants and fish in the pond are not active yet, the algae are the only organism actively contributing to the pond’s ecosystem. Since this algae has no competition, everything is perfectly set up for a bloom of suspended algae.

Suspended Algae

Typically, this condition clears up in a week or two when the temperatures rise enough for beneficial bacteria to colonize in the rocks and the biological filter. The rising temperatures will not only help start the production of bacteria in the filter, but it will also cause water plants to become active. As the plants begin growing, they will consume some of the excess nutrients and compete directly with the algae, reducing its growth.

String Algae

String algae can be a major issue all season long. There are different elements in the pond can encourage the growth of string algae. Sunlight, a heavy fish load, and failure to have enough plants in the pond can all contribute to string algae blooms.  String algae consume excess nutrients in the pond such as phosphates and nitrates. Plants in the pond compete directly with string algae for excess nutrients. By having plenty of plants in the pond, you can starve string algae.

The Easy and Natural Way to Control Algae 

The prevention of algae is made simpler by reducing the amount of nutrients available for the algae to feed on. This is all about having a balanced pond and a proper filtration system. A balanced pond is less likely to have algae problems. There are five factors that are necessary to achieve a balanced ecosystem. Removing any one of these items will make it much more difficult to keep a pond with clean, clear water.

These five elements are absolutely vital to have in your pond in order to reduce the amount of nutrients and keep your pond algae free:

Plants: Plants have a variety of benefits in and around the water garden. In addition to looking beautiful in the pond and in the landscape, water plants help control algae. They do this by consuming the nutrients in the water that algae would normally consume. Also, there are many plants that add oxygen to the pond that help improve the ecosystem. Some plants, such as water lilies, provide shade for the pond reducing the amount of sunlight available for algae growth.

Fish: Large fish like koi will eat a tremendous amount of algae. Koi constantly forage for food among the rocks and gravel in the pond, cleaning them of any algae that may be growing on them. Large koi are a definite asset to have in the pond.  They love to eat string algae.

Rocks and Gravel: When rocks and gravel are added to a pond, bacteria will colonize in the on the surface area of the rocks. Rocks and gravel provide a much larger surface area versus a smooth liner, so there is a larger habitat for bacteria to colonize and multiply. Once bacteria colonize the pond rocks, the biological filter in the pond increases.

Mechanical Filtration: A pond skimmer, vanishing edge, or intake bay acts as a mechanical filter by removing leaves and other debris from the surface of the pond before it can sink to the bottom. This means that debris can be collected and removed from the pond instead of falling to the pond floor and decomposing.  Decomposing organic material will lead to more nutrients for algae to use to grow.

Biological Filtration: Having the proper size of biological filter is essential if you want clean, clear water. Without a biological filter, you are facing an uphill battle against green water. An Aquascape’s BioFalls® Filter or a custom wetland filter will provide a huge area for bacteria and enzymes to colonize. These bacteria and enzymes consume nutrients and help break down organic debris and fish wastes that would otherwise contribute to water quality problems.

Nutrients From Outside the Pond

Another important factor to guard against is the use of chemicals or nutrients entering the pond from outside sources. There are several ways that nutrients can find their way into the pond. The two most common ways are storm water runoff and lawn fertilizer. Storm water runoff that’s allowed to enter the pond will quickly add additional nutrients to the ecosystem. Lawn fertilizers accidentally sprayed into a pond can quickly turn the clearest pond green. Avoid having lawns chemically sprayed or treated next to a pond.


Beneficial bacteria will help control algae. Beneficial bacteria feed on the same nutrients that algae does.  Adding nitrifying bacteria will help with green water. Nitrifying bacteria converts harmful fish wastes into nitrite, and then into nitrates.  Plants use nitrates for nutrition or fertilizer. Bacteria colonize on the filter mats and bioballs in the biological filter, as well as on the rocks and gravel in the pond. This will help the water stay clear.

Taking the proper measures can reduce the occurrence of algae. It is important to remember that algae are a part of nature and are an important part of the pond ecosystem. A pond is an ecosystem that supports fish, plants, frogs, birds, dragonflies, and lots of other wildlife. The main goal in keeping clean water is not to attempt to completely rid your pond of algae. Instead it is to keep it in balance with nature!


Just Add Water is an Ankeny, Iowa based landscape contractor specializing in water garden design, installation, renovation, and maintenance.

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