An Introduction To Suspended Pond Algae And Blanket Weed String Algae

Why Has My Garden Pond Water Turned Green & Developed Sting Like Weeds?

Pond Algae is a generic term used to describe many different forms of algae, found in garden ponds, including green algae, blue algae, brown algae, filamentous string algae, blanket weed, hair algae and pond scum. Some forms of algae are beneficial to the pond eco system but others are a major nuisance and given ideal conditions will cause the death of your pond fish.

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Algae are single celled primitive aquatic plants, closely related to fungi. Unlike their larger cousins algae do not have roots or stems. Algae grow in both fresh water and salt water. There are three forms of algae: planktonic, filamentous and macrophytic.

Planktonic Algae Types

These are unicellular organisms that float around the pond in vast numbers. They are microscopic and grow to about 4 microns (4 millionths of a meter) in diameter. Planktonic algae are responsible for algae blooms, also known as green water.

Common types include Chlamydomonas, Chlorella and Euglena species. They multiply rapidly given excess pond nutrients and sunlight (nitrates and phosphorus) by means of spores, cell division or fragmentation.

Filamentous algae Types

Filamentous algae have a thread like appearance, due to a series of cells joined end to end. This algae species is sometimes known as pond moss because they form fur like growths on any available pond surface. Horsehair algae, also known as Pithophora is a common pond variety that multiplies rapidly and tends to grow on the pond floor.

Of the filamentous algae varieties the most annoying for pond keepers is the Cladophora glomerata blanketweed variety. This green, slimy algae will readily attach itself to any available pond surface including side walls, pond filters and submersible pumps. There are over 150 different species of Cladophora. Blanket weed is capable of growing at phenomenal rates. It is not unheard of for blanket weed to grow up to 6 feet a day.

Other species of blanket weed that cause problems for pond keepers are the Rhizoclonium and Enteromorpha Spirogyra varieties. The Spirogyra genesis consists of approximately 400 species. Spirogyra filamentous algae appear as a tangled pond scum. During hot weather conditions and sunny spells they will float on the surface of the pond water. As the sun disappears the tangled pond scum sink again as oxygen production stops or slows down. At night time photosynthesis no longer takes place. Spirogyra algae start to use up oxygen in the pond, producing carbon dioxide. In densely populated ponds the rapid increase in carbon dioxide can lead to rapid increases in pond pH, resulting in an increase in ammonia levels. This rapid increase in ammonia will sometimes lead to fish fatalities.

Macrophytic Algae Forms

This 3rd category of algae look like true plants. They appear to have stems and leaves. They also attach themselves to the bottom of the pond and items placed in the pond. The genus Chara is a typical macrophytic algae or algal plant. High levels of calcium carbonate or bicarbonate in pond water favor this type.

What Causes the Build Up Of Pond Algae?

Large colonies of algae grow when the pond water contains large quantities of nutrients (nitrate and phosphorous), temperatures are high and there is an abundance of sunlight. Nutrients enter into the system through metabolic activity such as the nitrogen cycle and decomposition of organic matter, as well as from other sources such as the use plant fertilizers or regularly topping up tap water.

How Do The Various Pond Algae Types Affect My Pond?

The suspended algae variety multiplies at a rapid rate and due to its microscopic size can not be removed from your pond by your biofilter. The only really effective way of controlling this nuisance is to use a UV sterilizer or UV clarifier, which uses ultraviolet light to damage the outer membrane, causing the algae to clump together. This creates a much larger mass, which is easily filtered out of your pond by a bio filter.

Blanket weed and string algae varieties, multiply rapidly and form long, slimy clumps that attach themselves to any available surface. They consume large quantities of nutrients and will tend to be a dominant species. Once blanket weed forms in your pond it is almost impossible to get rid of. Barley straw is commonly used to prevent the growth of blanket weed, with some success. Unfortunately UV light does not destroy filamentous algae varieties.

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Too Much pond algae is Bad For Your Pond

If pond algae is not controlled the pond will appear untidy, dirty and will often smell.
As algae blooms and other algae varieties die off they fall to the pond floor where they start to decay. The decaying process produces carbon dioxide. The increase in carbon dioxide acts as a food source for the remaining algae, starting the process off all over again. In addition the carbon dioxide that is used up by the algae increases the pH level of the water. This increases the level of ammonia and decreases the level of ammonium. Ammonia is potentially lethal to aquatic life forms in high doses.
Any decaying organic matter, including pond algae uses up valuable oxygen as part of the rotting process. Oxygen is critical to the survival of aquatic pond life and nitrifying bacteria that use oxygen, in large quantities to breakdown ammonia.
The rotting algae clumps (pond sludge) also produce ammonia. This places more strain on the pond filter that houses the nitrifying bacteria.

Methods commonly used To Control Pond Algae

The most successful and in my opinion the only really effective method of controlling floating planktonic algae is to use a UV sterilizer or UV clarifier. The UV light destroys the cell walls, causing the suspended algae to stick together, forming a larger mass than can be removed by a pond filter or pond skimmer. Remember that single cell living floating algae are microscopic life forms that will simply pass through the biofilter, due to their minute size.
Hit the algae where it hurts! Where ever possible try to remove as many of the nutrients as you possibly can. After feeding your fish, remove uneaten fish food. Use a pondvac to remove pond sludge. Install a pond skimmer to remove leaves and other debris that falls into the pond water. Do not over feed fish as anything surplus to their growth and development needs will be excreted into the pond as solid and liquid waste. Place aquatic plants in containers of aquatic compost, surfaced with shingle.
Aquatic plants are a great way to reduce the levels of nutrients in the pond water, as they use them as a food source and compete with pond algae. Try to cover at least one third of the surface area with aquatic plants. Oxygenating plant varieties will also add much needed oxygen to the pond water.
Perform routine cleaning by removing blanket weed and string algae with a rake. Duck weed is easily removed with a pond net.
The use of barley straw extract will help to inhibit the growth of BLANKET WEED algae growth. Barley straw bales are best placed in the pond in early spring, where the natural decomposition releases chemicals in preparation for summer when nutrients and sunlight are at their peak.
The Centre for Aquatic Plant Management has discovered that ultrasound waves are proving to be one of the best solutions in the fight against blanket weed. The ultrasound breaks down the cell walls, causing death within 3 weeks. This is at present an expensive treatment and requires specialist installation.
Some pond keepers use pond water treatments to treat pond algae, in particular the floating algae varieties. I am against the addition of chemical treatments as it is easy to overdose, it is a quick fix that only has a minimal effect and can interfere with nitrifying bacteria.

To conclude I would like to add that some pond algae is beneficial to the pond, as it provides a source of food for fish, provides shade from the hot sun and provides a hiding place from heron, king fishers and other predatory birds. It is natural to have some algae growth on pond surfaces, pond filters, pond pumps, pond tubing, pond rocks and almost any available surface within the pond. The secret is to keep it under control.

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