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Controlling algae and duckweeds
The long term solution -
prevention
Reduce nutrient levels by: removing bottom sediments;
preventing soil or fertiliser running into the pond; and using rain
water, not tap water, to top up the pond in summer.
Natural Predators
Populations of zooplankton (such as water fleas) build up naturally
during the spring and eat the algae.
Manual clearance
Clear blanket weed using a rake,or by twisting it on a stick.
Duckweeds and Water Fern can be scraped from the surface
using a board or a sieve. Compost the plants away from the
pond.
Encouraging submerged plants
Submerged aquatic plants (often called oxygenators) can help
soak-up the pond’s nutrients. However, many native submerged
plants will not grow in nutrient-polluted water, so only add them
when you have improved the water quality.
Shade
Shade can reduce problems with algal growth, so locate your
pond in a shady spot. Larger leaved floating plants can also
provide shade on the water surface.
Barley straw
Barley straw rots down to produce a range of chemicals that kill
many types of algae. It takes up to a month to become active,
and it’s best to add it in spring and remove it when it has turned
black, about six months later. However, barley straw is not a cure,
so applications will need to be ongoing.
Pond filtration systems
You can buy a wide range of pump and filter systems that will
remove nutrients and algae from the water. There are a number
of different types, including biological filters and ultraviolet (UV)
light-based systems. These can be run alone, or if you have fish, in
combination.
Pond dyes /colorants
Pond dyes work by blocking some wavelengths of light, so that
algae cannot grow. The dye degrades naturally over a number
of weeks and then needs to be reapplied to remain effective.
Although non-toxic to animals, these dyes will also kill your other
submerged pond plants!
Other treatments
There are a number of other products containing enzymes,
bacteria and minerals available for reducing blanket weed and/or
algae in your pond. To be effective always follow the instructions.
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