Algae Control and Algae Maintenance in Ponds

Wherever water is being stored, algae problems might occur.  Stagnant water with high temperature or high concentration of Nitrates and Phosphates has the possibility of creating algae bloom. Green algae can make the water unclear and blue-green algae can cause foul odour and even pose a health risk. It is therefore important for pond owners to plan and implement algae control measures.

What Factors Increase Risk of Algae Problems?

No pond is ever totally free of algae but in a balanced environment, algae can be controlled. Through photosynthesis, algae combine water and carbon dioxide to form sugars and energy for growth. Algae produces oxygen but when the sunlight is not available (at night), they respire. This respiration process uses the stored sugars and available oxygen to form carbon dioxide, which starts depleting the oxygen of the pond. There are two types of pond algae:

Green Algae: These single-celled organisms, which remain suspended in water, are so tiny that they pass through even the finest filter. If conditions are right, meaning there’s plenty of nutrients and sunlight, as many as five million algae cells per milliliter of pond water can be present.

String Algae (also known as “hair algae”): This filamentous species, which grows in long strands, adheres to rocks and waterfalls. They eventually tangle together, forming thick, unsightly mats that can double their weight within 24 hours.

Some of the biggest factors that increase the risk of algae are:

  • High light levels and high water temperatures stimulate faster growth. Avoid shallow water in ponds.
  • Still water and poor water circulation. Limited wave action and movement favors algae growth.
  • Excess nutrients, especially phosphorus and nitrogen are a fertilizer source for algae. Runoff from fertilized fields, lawns or pastures can create excess nutrients.
  • High pH or alkaline water increases the risk of algal blooms.

Implementing best practices in the construction and maintenance of ponds which counters or alleviates the factors listed above will help reduce the risk of algae bloom. No pond is ever totally free of algae, but in a controlled environment, algae can be kept in check.

Algae Control and Management

In order of importance we can classify algae control into 3 groups.

  1. Physical/mechanical Control

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 per day and therefore you need to calculate your pond volume.

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. The filter needs to run 24 hours a day 7 days a week to work properly. Filters generally have a maximum and minimum flow rate requirement.

Of vital importance is the circulation of the water. If areas of the pond do not receive sufficient flow, then chemicals used for treatment of the algae will not be effective in those areas. Ponds with irregular shapes and estuaries will require specifically designed distributed flow systems for effective algae control. Furthermore, stratification of the water due to surface heating from the sun can cause the chemicals to flush over the surface without contacting algae situated of the bottom of the pond.

A number of the chemicals used for treatment of algae are degraded by the sun so the diurnal timing of treatment and circulation also plays an important part in the treatment program.

Close circuit ponds with water recycling can have advantages in some applications as the environmental impact may be easier to deal with, and chemical costs can be lower compared with open circuit systems where a permanent fresh water supply is used.

Physical controls also involve raking or dredging, or machine mowing the pond.  And to ensure clear water all year round, an ultraviolet sterilizer is highly recommended.

  1. Chemical Control

This involves applying chemical algaecides. Chemical controls help keep algae under control but do not prevent algae problems if conditions remain favorable. Chemicals can be expensive, and safety issues are involved for the applicator and for your operation if applied incorrectly.

To determine the most effective material, you should first identify the type of algae present. Filamentous (mat-forming) algae are the most common form found in ponds. They consist of long strands and can form into a mat on the pond surface. Once you decide on chemical controls, it is wise to choose an algaecide and have a maintenance program ready before very high levels of algae become established.

Chemical algaecides include oxidants and hydrogen peroxide compounds (relatively new products), as well as copper salts and other copper compounds (which have been the old standbys). Hydrogen peroxide compounds are organic and break down into water and oxygen. These products can be as effective on algae as copper, but are much less effective on some of the more difficult-to-control species.

Copper is a heavy metal and never decomposes. Although copper builds up in pond sediment, when copper products are used at concentrations according to the labels, there have not been adverse effects. Copper can control the algae species that are present, opening a niche for copper tolerant algae. Therefore, preventive measures are very important.

Additionally, there are dye materials (which eventually photo degrade) that block portions of the light spectrum that algae require to photosynthesize.

Material/ Active Ingredient Copper Sulphate in Varying ConcentrationAcid Compounds of Varying Concentration (Typically Acid Blue and Acid Yellow 23)Sodium Carbonate Peroxyhydrate (Sodium Carbonate + Hydrogen Peroxide)Elemental Copper from Mixed Copper Ethanolamine Complexes
(E) – Excellent
(G) – Good
(S) – Satisfactory
Filamentous (E)
Branched (E)
Planktonic (E)
Filamentous (E)
Branched (E)
Planktonic (G)
Filamentous (E)
Branched (G)
Planktonic (E)
Filamentous (E)
Branched (E)
Planktonic (E)
Mode of ActionDisrupts cell membranesBlocks portion of light
spectrum necessary for
Likely disrupts cell
membranes and walls
Disrupts cell membranes
Estimated Dosage Rate250g – 2000g / million litres800ml/ million litres1kg – 7kg / million litres2 litres – 12 litres / million litres,
depending on product
Usage DetailsLess effective in hard water

(high Ca and Mg
content). Toxic to fish at low pH.

Best when water
temperatures are above 15degC.

Use early in season
before extensive growth.
May not work well in shallow areas less than 60cm – 1m deep.
Best where water pH range is 6.8-7.8. Works at all water temperatures,
but faster at warmer temperatures.
Chelated copper
compounds prevent copper from precipitating
out of solution in hard water.Best when water
temperatures are above 15degC.
Relative Cost$$$$$$$$$$$$$$


Some chemical treatments do not actually harm the algae, but treat the pond conditions that may otherwise stimulate algae growth. In ponds with a high pH there are various chemicals that help to make the pond water more acidic. Activated Carbon products can also be added to the pond to absorb excess nutrients and so reduce the available food.

  1. Biological Control

Biological algae control is essentially through the addition of aquatic plants that compete with the algae for light and food. Beneficial bacterial cultures could be added to the pond water. Some of these cultures help to decompose the organic matter, such as leaves and organic waste, while others consume the nutrients that the algae feed on.

For further information about water filtration and maintenance of your ponds, please contact us to speak with one of our specialists.


Articles and information from The State of Queensland (Department of Agriculture and Fisheries)

Controlling Algae in Irrigation Ponds’ by Diane M. Camberato and Roberto G. Lopez, Purdue Horticulture and Landscape Architecture