The reason why algae needs to be eliminated is twofold, yes it is unsightly but perhaps more important, it has a detrimental effect on any pond life.
There are many types of algae including blanket weed that turns a pond into something resembling pea soup. This creates a problem as the algae de-oxygenates the water, hence the need to eradicate it.
What Causes Pond Algae?
Too much sunlight is a major reason, particularly during the summer and especially if the water is too shallow.
The other most important factor is high nutrient levels when poor filtration fails to deal with decaying matter, rain leaching garden fertilizer into the water or the detritus from too many fish.
How Can You Prevent Algae?
Position the pond away from trees and, especially in the autumn, use netting to prevent leaves falling into the water. Also make sure that the dying foliage of aquatic plants is collected to stop it decaying at the bottom of the pond.
Ensure that the pond receives some shade during the day. If you have a south facing garden this can be difficult but it's really important and one way to achieve it is having surface plants such as lilies cover 50% of the water
The water should be at least 2ft deep, ideally 4ft if you are keeping fish and ensure that the pond is not overstocked with fish. Avoid the water becoming stagnant by installing a water feature that will aerate the pond.
Only introduce plants that are growing in low nutrient aquatic compost and, when topping up a pond, use rainwater from a butt rather than tap water.
Regularly use a pond test kit to discover the water's pH and levels of ammonia, nitrate, nitrite, chlorine. By detecting any problems you can take remedial action and return the pond to the balance that's best for aquatic life to flourish.
Adequate filtration is essential to prevent the build-up of nutrients. There is a wide range of pond filtration equipment, some with integral UV clarifiers that eradicate algae, leaving the filter to remove other debris. Pond UV clarifiers can also be bought separately.
Eliminating Algae From A Pond
Do not be tempted to replace the water, the chlorine and other substances in tap water will only make the problem worse in the long term.
If algae has already taken a hold on the pond remove as much as you can with a stick or net and then use a specialist pond treatment that will either kill the algae or remove the nutrients that the algae feeds on. Barley straw can also be effective, for a small pond use it in liquid or pellet form.
Once under control, put into place the algae prevention advice and then periodically test the water as you may well need to treat it on several occasions. With regular attention the pond should remain in perfect condition for you to admire and for your wildlife to thrive in.