build a fish pond

You are here: Home > Build a Koi Pond > Water Quality > Pond Algae Control

Pond Algae Control

Like all plants, algae require nutrients to grow and reproduce. Because algae are free-floating, they must get those nutrients from the water. They have no ability to obtain them from the pond bottom. Thus, the higher the nutrient level in the pond, the more algae you will have. At slightly higher nutrient levels, the algae community is often dominated by filamentous algae. This is particularly true during summer. At very high nutrient levels, the algae blooms are typically composed of planktonic algae rather than filamentous algae.

Green Pond Water Algae Control

Pond Water swarms with a variety of microscopic organisms. Of the vast majority of fish ponds owners are blissfully unaware. Those that you cannot miss are the ones that discolor the water. As your pond becomes increasingly fit to support life it will develop the slightest tint of pale amber (this is the color it should be). The color of your water will help you decide what the problem is and how to correct it.

Green pond water is caused by single-celled free-swimming algae. They are individually microscopic but may be present in such numbers to make your pond water look as if it is filled with green distemper.

For their existence they depend on light and mineral salts, both of which are abundantly available in a newly filled small garden pond in which plant growth is still relatively undeveloped. So it is entirely natural for the new pond to be pea-soup green within a week or two of being filled.

If your pond is not new it has an excess of nutrients in the water, coupled with a lack of plant cover on the surface of the pond. Excess nutrients can be the result of overfeeding, overstocking with fish or a lack of filtration. In a pond where everything is balanced with the correct level of fish and plants, pond water should be clear.

Green pond water will clear with submerged oxygenates and surface covering plants. The surface cover of water lily and other leaves cut off sunlight at the surface and is an effective pond algae treatment.

Single-celled algae swarming in the upper water layers where light intensity and warmth are greatest begin to find it hard to survive. Starved of food and deprived of light they die and sink to the bottom. The pond water clears, and it very often happens quickly, overnight.

The keys to a balanced system are:

  • A Pond of the Proper Depth
  • A Good Pond Filtration System
  • Having A Balance of Plants Fish
  • and using a UV Clarifier

Mosslike algae that grow on the side of the pond are beneficial and a sign of good pond health. Because they harbor the same kind of bacteria found in an artificial biological filter, they help to remove toxic chemicals from your water.

It is important to avoid the urge to empty a pond full of green pond water. Although this may seem the sensible thing to do for algae control, nothing could be further from the truth. Emptying the pond water will temporarily alleviate the green pond water situation, but minerals in tap water will cause the refilled pond to become thick with algae very quickly. These salts and minerals are one of the causes of algae and take a long time to break down. The recipe for clear water is simply plants and patience. It is generally ponds with insufficient plant growth that experience pond algae problems.

Once the water has cleared it should stay that way except, for a brief outbreak in spring. In winter the top water layer becomes cold, sinks, and forces the richer bottom layer of water upwards. This results in nutrients being present in the upper water layers to nourish a fresh outburst of algae when the weather turns warmer in spring. It lasts only until the new season’s growth of oxygenates and water lilies get going.

Green pond water problems are inherent in some water pond designs. If the small garden ponds is a shallow saucer, or has a very large shallow-water area and a small area only of deeper water, then the volume will be small in relation to the surface area and algae of one sort or another will be a constant headache unless the surface is almost completely covered.

Sometimes it may not even be your pond that is causing the problems. Check to make sure you are not getting run off from your lawn or a neighboring lawn, this could cause an algae bloom.

Remember that Koi are plant eaters, and it’s healthy for them to eat the algae off the sides and bottom of your pond.

Click Here for the Aquatic Weed Control Chart List of Weeds and which Algaecides or Herbicides to use.

Pond Algae Types

There are thousands of species of pond algae. All are plants, using chlorophyll for photosynthesis. Chlorophyll is the green pigment found in plants and found abundantly in nearly all algae. Chlorophyll allows plants and algae to use sunlight in the process of photosynthesis for growth.

Listed below are some common Pond Algae Types:

String Alage

String algae is a problem suffered by most artificially filtered ponds. It is caused by an imbalanced pond metabolism and occurs because the rate at which nutrients such as phosphates and nitrates enter the pond is unnaturally high and out of balance with the rate at which they are broken down.

Excessive food relative to pond volume results in an accumulation of nutrients on which string algae thrive, boosted by abundant sunlight in a clear pond. In a natural lake or pond, the growth of string algae is kept in balance by the restricted amount of nutrients. In addition, many organisms graze on string algae, preventing it from growing out of hand.


Blanketweed, thread algae, silkweed and filament algae are all different names for basically the same type of pond algae. Most commonly known as blanketweed, this algae is made up of many different species of filamentous algae. Blanketweed is often seen clogging pond filters and tangling itself around pond plants, notably oxygenating plants.

In a balanced pond, although there may be signs of blanketweed, it rarely becomes a problem. However, as most pond owners struggle to reach a natural balance, or make no effort to achieve it at all (as in Koi ponds), blanketweed can become an unsightly nuisance.

Blanketweed can thrive in many different conditions, but does best in well-lit ponds that are high in nutrients. Ponds with little or no plant life are often plagued by blanketweed problems.

Although filtering a pond will help to control free-floating algae, it will not aid the removal of blanketweed. Indeed, the increased use of pond filters and ultraviolet sterilizers raises the chances of a blanketweed problem in a pond, as these filters will provide clear water, high in nutrients through lack of competition from other forms of algae.

There are many methods of tackling blanketweed and most are successful, at least for a while. However, it does appear that this form of pond algae becomes resilient to certain forms of pond algae control over time.

Algicides are the easiest and quickest method of trying to remove blanketweed. They vary from simple light inhibitors to complicated pond chemicals designed to kill the blanketweed. Be careful when using algicides and follow the recommended dosages. Be sure to remove as much blanketweed as possible (by hand) before treating the pond. As the pond algae dies off, remove it as quickly as possible. Large growths of blanketweed dying off in the pond can cause water quality problems, so monitor the ammonia and nitrite levels while using any method of killing blanketweed.

Filamentous algae

Filamentous algae is one of the most common aquatic weed problem in ponds. Its "sudden" appearance as it floats off the bottom causes consternation to pond owners as it degrades the aesthetic and recreational value of their ponds. Additionally, large amounts of filamentous algae can lead to a fish kill if specific climatic conditions occur.

Planktonic Algae

Plankton algae is commonly known as blue-green pond algae, scum, or a waterbloom. It is located lakewide and is generally free-floating, but concentrations occur along windward shores and backwater areas.

Plankton pond algae provides food for certain small aquatic animals and young fish. Abundant growth indicates that a lake has excessive nutrients, usually phosphorus.

Planktonic Algae in Ponds pdf. (Right click to download.)

Duck weed


Duckweeds and Watermeal is commonly known as lesser duckweed, duck's meat, or water lentil.

Duckweed is a very frustrating weed. It can easily find its way into your pond by other plants or by birds (hence the name). Only a single fragment is required, and under the right conditions it will rapidly divide and quickly cover the whole pond. This can deprive beneficial beneficial submerged plants of light and even prevent gas exchange in still water ponds, leading to toxic conditions and the "bad egg" smell. If you have Koi or goldfish in your pond, they love to eat duckweed. Just reduce the amount of food you have been feeding to encourage them to eat the duckweed.


Spatterdock is commonly known as a yellow water lily, yellow cow lily, and pond lily. It is located in sheltered areas, such as shallow waters with muck or silt bottoms.

Spatterdock is a rooted plant with bright yellow flowers that extends slightly above the surface. The flower is surrounded by a heart-shaped leaf. The leaf is grass-green colored, 8 to 16 inches long, and may float or extend above the water surface. The petiole (leaf stalk) is mostly below the surface.

The spatterdock flower forms a yellow sphere with petals that curve inward. The flower rises several inches above water. Spatterdock fruits are eaten by waterfowl and muskrats. The underwater roots contain starch and are edible.

Because spatterdock is a valuable and decorative plant, removing it may allow less desirable plants to move in.


Spirogyra, the melodic name of which derives from its spiral bands of chlorophyll, it consists of long strings of cells that attach themselves to the pond bottom and other surfaces. It is moss like algae that grows on the side of the pond, it is beneficial and a sign of good pond health. This type of algae harbor the same kind of bacteria found in an artificial biological filter, they help to remove toxic chemicals from your water.

Pond Algae Control Remedies

Pond Algae Control remedies are numerous, there are mechanical, biological, and chemical control measures, each with their own advantages and disadvantages.

The sudden depletion of nutrients to a pond with a severe ongoing algae bloom could cause a summer fish kill. In this case, it makes sense to allow cooler fall weather to decrease the algae bloom and then implement a plan to prevent new blooms the next year.

In some situations, it may be impossible to eliminate or substantially reduce unwanted nutrients from entering a pond. A preventative control method is the use of an aquatic dye to prevent initial growth early in spring. The dye must be added by April 1st to insure prevention of that year’s algae blooms.

As "old" algae cells naturally die off, few new algae cells are produced and the algae population is controlled as long as the compound is being produced.

There are thousands of species of pond algae types. All are plants, using chlorophyll for photosynthesis. They all need, to varying degrees, water, light and nutrients, and there is usually no shortage of any of them in a fed fish pond.

Over feeding your fish is one of the fastest ways to develop a pond algae bloom. Feed your Koi only what they can eat in 3 to 5 minutes twice a day, this is the most benefical way to feed your Koi. If there is any food left after feeding, always remove it.

If you let organic matter accumulate or offer excessive food, the resulting population explosion of heterotrophic bacteria will lead to an algae break out and green pond water.

Commercial products are available to eliminate the excess organisms that flourish when you make the mistake of overfeeding.

Vegetable filters are used in a number of small garden ponds. Freshwater plants such as watercress are good nitrate removers. The drawback is that they need to cover a large surface area, even in a relatively small garden pond.

Tools for Removing Algae

You can use your bare hands if you wish, but the following items will also extract algae from the water:

  • a long stick or broom handle.
  • a net.
  • a toilet bowl brush.
  • an "algae twister" gadget, a long stick with two sharp toothed metal circles at the end.
  • a small, thin tined rake (a gardening tool for children).

Always dispose of algae properly by digging it into a garden bed elsewhere in your yard or adding it to the compost pile - do not dump it in nautral or man made waterways, where it can grow to become a bigger problem.

Realize that physically removing algae from your pond is a temporary solution. It will make your display look better for a while, but if you don't address the cause of the bloom, more will grow to replace that which you have extracted.

Copper sulphate is not recommended: it works, but it is too easy to overdose and kill your cherished pond plants as well as the algae. Hydrated lime works in some ponds and has disastrous effects in others.

Success requires particular conditions of water chemistry, including pH, and if the conditions are not right all fish in your pond will die. Algae treatments should always be considered as short-term measures. For a long-term solution, look at balancing the nutrient level in the pond with correct planting, filtration and stocking of fish. When using algae products it is important to monitor water quality, as there is a danger of deoxygenation caused by the algae dying off and decaying.

Before adding algae products, change 10-20 percent of the water to remove a proportion of the dead algae and reduce the likelihood of pollution of the pond. As an alternative strategy, use very fine foam or pad in the pond filter to remove small algae particles. A little secret that I have used in my pond filter is pillow filling, this works great!

UV Clarifier

Another way for Pond algae control is with a UV clarifier. There are a lot of misconceptions regarding the use of UV in water gardens. One concern is that you will sterilize your pond and kill all of the beneficial bacteria. This is impossible. Not all of the water will pass through the UV in one circulation and there is always going to be beneficial bacteria inside your biological filter and on everything in the pond, including the liner. What the UV will do, when properly sized for your pond and flow rate, is reduce some bacteria, including harmful bacteria, as well as microscopic organisms that could be harmful to your fish. It will also destroy the DNA in single cell algae cells thereby killing it very efficiently. This will provide clear water when the turbidity is due to suspended algae. UV provides 100% success for achieving clear water from single cell algae in a pond.

Algae can be hard to get a handle on if you don't tackle it when you first see it.

pond algae types

You are here: Home > Build a Koi Pond > Water Quality > Pond Algae Control

Share |

The Only Koi Book You Will Ever Need!

Whether you are a beginner or a Koi pond specialist this ebook contains all you need to know to have a beautiful, optimal ecosystem, with healthy pond fish!

~Price $20.00

Pay with Safe and Secure Pay Pal.


After Check out you will be taken to a page to download your Ebook.


Cattails are located in marshes, ditches, shorelines; shallow areas of lakes, ponds, and slow streams, or any quiet water up to 4 feet deep. They grow above the water surface, and are thickly rooted. They have long slender stalks growing 3 to 10 feet high. The flower consists of a cigar-shaped “cattail” which is green during early summer and turns brown and fuzzy in the fall and following spring.

Here is a pdf file you can download that has a list of the REGULATED NOXIOUS AQUATIC WEEDS Click Here.

Algae Defintion

Algae are a wide variety of tiny, often microscopic, plants (or plant-like organisms) that live both in water and on land.

Phytoplankton Algae

Phytoplankton are microscopic, free-floating aquatic plant-like organisms suspended in the water column. They are sometimes called planktonic algae or just algae.

Though individual phytoplankton are tiny in size, they can have a major influence on a waterbody. For example, phytoplankton abundance often determines how biologically productive a waterbody can be; small amounts of phytoplankton often result in less fish and wildlife. Also, an abundance of phytoplankton, will significantly affect your water clarity.

Enjoy This Site?
Then why not use the button below, to add us to your favorite bookmarking service?

Build A Koi Pond Blog
RSS Feeds

Twitter Button

Pond Algae Control Beginning

Contact Us

PayPal Acceptance Mark

Return to top
Copyright© 2008-2030.Koi-Pond-Guide.com