Blog | Water Garden Ltd - Green or Dirty Pond Water? Treatments explained...

Green or Dirty Pond Water? Treatments explained...

12th June 2013

Water treatments for pond and lakes can be used to great effect, in order to tackle specific water quality problems.  Here’s a brief run-through of the most common problems, together with specific treatments and solutions to help solve the issue.  You’ll notice that some of the water treatments discussed below help with more than one issue, so these are ideal for keeping on-hand should problems arise. 

You can view our full range of Pond Water Treatments here.  You can also click on any of the pictures below for more details on each problem and suitable remedies.

Green water. 


If the water is looking more like a bowl of pea soup than an attractive decoration, then the likely cause is single-celled suspended algae.  The very best method of tackling this problem long term is the use of an ultraviolet clarifier and pond filter.  The UV radiation will cause these microscopic organisms to clump together into larger particles, which can then be removed by the filter system.  If you are unable to invest in a filter system or cannot access mains electricity near to the pond, here are a few specific water treatments to curb the issue.

Green Water Solutions.

  • OASE Pond Clear.  Causes fine organic waste and single celled algae to drop out of suspension, which can then be removed from the base of the pond with an algae net or fine mesh net.
  • OASE String Algae Control.  Versatile water treatment which will help to tackle green water but also String Algae (blanketweed) and Duckweed.
  • Extract of Barley Straw.  Natural water treatment for clearing single celled algae and string algae.
  • VAqua Algae Control.  Completely natural, biological water treatment for ponds.  Consists of 2 strains of ‘friendly’ bacteria to suppress and digest algae and rotting biomass on the pond floor.  VAqua can also be used in very large ponds and lakes.  We recommend implementing a means of adding oxygen to the pond if possible to sustain the growth of this water treatment.
  • Also see;  Ultraviolet Clarifiers.


String Algae.


Commonly known as Blanketweed or filamentous algae, these long hair-like strands can grow very rapidly around the pond or lake perimeter, gripping on to pond walls and liners.  Pond Filters cannot tackle this issue as the algae is not able to pass through the pump due to the algae congregating and attaching itself in shallower water zones.  String Algal blooms usually occur in early spring or late autumn and generally in clear water.  As with single celled algae, the fundamental reason is usually excess nutrients on the pond floor which becomes the food source.

String Algae Solutions.

  • OASE String Algae Control.
  • Extract of Barley Straw.
  • VAqua Algae Control.
  • Also see;  Pondovac Pond Vacuum Cleaner.  Ideal for removing dead or dying algae from the pond perimeter but can also be used to extract any organic waste at the base of the pond, helping to remove the nutrient-rich food source.


Cloudy or Dirty Water.


Murky pond and lake water is usually caused by sediment being stirred up from the floor, either by fish or a circulatory pump.  If you already own a pond vacuum cleaner, try to remove as much of this debris from the pond as possible.  As this is often very fine sediment, you should divert the water to plant borders (this is excellent fertiliser!) as this will pass straight through the vacuum cleaner sludge bag.  Once the small particles are removed, the vacuum cleaner can be used with the collection bag to trap leaves and larger debris which may collect later on.  The collection bag can be hung over the edge of the pond so that no water is lost in the cleaning process.

Dirty Water Solutions.

  • OASE Pond Clear.  Treats ponds up to 10,000 Litres per treatment.
  • OASE Pond Clear Bulk (treats larger ponds of up to 100,000 litres per treatment).




Tiny yet invasive plants which float on the water surface, Duckweed (Lemna Minor) can create a carpet of greenery in a very short space of time.  This carpet layer blocks sunlight from reaching pond inhabitants and also looks unsightly.  Once again, this is usually a sign excessive amounts of nutrient and debris on the pond floor.  A decorative fountain or aerating fountain can help to reduce the issue as Duckweed growth can be inhibited by moving surface water.  Fountains and aerators will also help to push some of the weed to the pond or lake edges, where it becomes easier to harvest.

Duckweed Solutions.

  • OASE String Algae Control.
  • Duckweed Buster.  Bacterial water treatment specifically developed to control Duckweed in smaller ponds.


If you need any further advice on what water treatment you require to tackle your pond or lake issue, please feel free to email or call us.  We’ll do our very best to help.

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