Pond Algae Solutionpond algae

Pond algae is the bane of many who enjoy keeping ponds. They basically act like plants and need both sunlight and nutrients like ammonia and nitrate to thrive. These nutrients come from the breakdown of organic matter such as leaves and grass, fish waste and uneaten fish food. There are thousands of different species of algae, but here are the most common types of pond algae:

  • Filamentous Algae – Also called “pond scum”, will appear on the surface of your pond in groups/mats.  You’ll also see it along the edges of your pond, and on logs and rocks.  It looks like threads of hair, but is actually a group of connected cells.  Common species are Cladophora, Mougeotia, Rhizo-clonium, Spirogyra, Hydrodictyon, and Zygnema.
  • String or Planktonic algae – Covers the surface of ponds.  Are tiny plants that are brown to pale green in color.  Will often produce a foul odor and depletes your pond of oxygen.  Also can be toxic to humans and animals.  Coming species are Scenedesmus, Chlorella, Anabaena, Oocystis, and Pediastrum.
  • Toxic Algae – A green-blue colored species that produces poisonous substances that could cause death or illness to humans, plants, and wildlife.  After contact or ingestion it could lead to headaches, rashes, nausea, vomiting, fever, body pain, or other irritations.
  • Colonial Diatoms – You’ll usually find this algae growing on concrete or sand around your pond.  Looking like grayish or brown covering.  Typically grown in colonies.
  • Resistant Algae – This algae has a protective mucilage that makes it algaecide resistant.  Can be with Pithophora or Lyngbya.  Pithophora is also called horsehair and is dark green in color.  Growing in clumps of coarse filaments that look like steel wool.  Most often found growing on the bottom of ponds.  Although can be found on the surface.  Lyngbya are clumps of many thousands of cells that are gray, black, or green in color.  Also usually found on the bottom of ponds, but also can be surface floating.

This article will help you create a simple pond algae control routine that will ensure a safe and clean looking pond. We will discuss several methods to remove algae from your pond to help keep your water clear. Along with the benefits and drawbacks of each.


Algaecide for ponds is like the nuclear weapon of pond algae removal: It is the fastest way to clear up your pond but also the fastest way to kill any other living thing such as fish and plants. The compounds found in chemical pond algaecides are harsh and some locations are even banning them (such as New Jersey). Another drawback is that the oxygen supply in the water will plummet because the algae that were producing oxygen are now dead.

As with any strong chemicals, please follow the directions carefully to avoid any horrible mishaps. You will also want to consider ways to add oxygen back into your pond. Any device that will move water around, such as a pond aerator, jets or fountains, that will increase oxygen and help control algae in ponds.

You should also remember that any dead algae that remain in the pond will simply become food for the next generation of algae. Chemicals are a quick solution but will not treat an underlying problem.

UV Filters/Sterilizers

UV pond filters or sterilizers are good at removing the type of algae which discolor water. The speed of water filtration determines whether you call an item a filter or a sterilizer. A UV filter shines UV rays into the water, so naturally, the speed of water filtration will determine how much light is absorbed at a given time. With UV light for pond algae, you should be able to see a difference in a few days.

Unfortunately, as with chemical algaecides, UV filters only hide the water quality problem. Often, the algae will come back in another form such as string algae which can’t be filtered. Therefore, UV should be used in conjunction with natural treatments which do work over the long-term.

Nature’s Way: Barley and Bacteria

Barley straw for ponds is a natural way to keep your pond clear. Farmers have been using barely straw to control pond algae for a long time. Rather than killing algae, decomposing barley changes the PH of the water and makes it less suitable for algae growth.

Keep in mind that barley is most effective as a preventative to algae growth. It is not going to kill off enough bacteria to make a dent in a bad algae infestation.

Furthermore, it is necessary to maintain a constant supply of barley in the pond. Many people like this method while others find it disappointing. For this reason, it is a good idea to use bacteria and barley together for best results after enough algae have been eliminated through the use of chemicals if needed.

If chemical treatments are like nuclear bombs, pond bacteria is like having an army constantly present in enemy territory. Bacillus bacteria is found in all Earth’s ponds and is nature’s way of maintaining healthy water. Bacteria work by outcompeting algae for pond nutrients; this keeps the algae from growing out of control.

Pond bacteria comes in both liquid and powder forms. What you need to think about more than deciding liquid versus solid is the number of bacteria in the product. This is measured in colony forming units, or CFUs. Try to aim for at least one billion CFUs. The higher, the better. Bateria is natural to pond environments, so overdosing is impossible. In fact, it will be necessary to add bacteria frequently as they have a growth cycle of around a month.

While not necessary, some people use products for bacteria to grow on like bio-balls. This idea is to increase the surface area of bacteria hitting the water so that they do a better job cleaning the water.

The best aspect of bacteria is that they can be combined with the other methods mentioned. After those methods are used, bacteria can be added to reduce future algae growth and is the best prevention. The only other thing to consider is using special winter-blend bacteria. It is made for lower temperatures and is helpful especially after leaves and other debris fall into ponds during the fall season.

Proper Fish Care to Reduce Algae

When you feed fish, are you feeding them or the pond algae? Fish like Koi actually need less and less food as the temperature drops. So be sure to research your fishes’ care and only feed them what they can consume in a few minutes. The interesting thing is that they might not even need food if the algae count is very high. This is because the fish will feed on algae as they do in the wild.

Finally, if you are serious about algae reduction, don’t keep too many fish in your pond. The more fish, the better filtration systems needed to keep algae at bay. As a general rule, new ponds should hold no more than an inch of fish per square foot. If your pond is more mature and has excellent filtration in place, you may consider adding a few fish. Increasing to 2 or 3 inches of fish per square foot may be okay.

Final Thoughts

If you are planning a new pond, do not place it in an area where it will receive full sunlight all day. Remember, algae need sunlight just like plants. Likewise, adding plants to your pond can also keep the ammonia and nitrate levels down because they will use it before the algae get a chance to.

As you can see, the best pond management methods for pond algae involve working with nature. By using UV light, barley, plants and bacteria, you will be establishing a healthy eco-system. Consider using chemicals sparingly or not at all.

We often say that if you have a algae problem, the best pond algae control solution is adding more perennial aquatic plants. 

Once you establish a healthy system, it will become an enjoyment rather than an annoyance. These tips will reduce maintenance time and give you and your guests a beautiful pond to admire.