Algae is a naturally occurring presence in almost all garden ponds. Although some algal presence can be beneficial, it can begin to grow at an alarming rate and is considered by many to be one of the biggest problems for pond owners.

As well as looking unsightly it can disturb the pond’s natural balance and effect the water quality. There are many varieties of algae, but these are generally split into two groups; suspended algae, or green water algae, and filamentous algae, or blanketweed.

Suspended algae are microscopic single celled species which cause algal blooms and can turn the pond water a ‘pea soup’ green. These blooms are more common in spring as the algae develop before most pond plants and take advantage of the increasing warmth, sunlight and surplus nutrients.

Like all plants, algae require sunlight to photosynthesise and nutrients, such as nitrate and phosphates to grow and develop. The natural remedy for ridding the pond of suspended algae is to keep a good stock of pond plants to out-compete the algae for nutrients. Adding shade to the pond with tall plants, lilies or a pergola will also hinder the algae’s photosynthesis and growth.

A common mistake when trying to eradicate suspended algae is to carry out a heavy water change in an attempt to dilute the algae. Water changing with tap water is one of the largest errors. Algae prefer slightly harder water, so if you are in a hard water area you will be improving the conditions for the algae. Tap water also contains nitrates which will be used by the algae as a fertilizer. Whatever method of water change is used, the increase in water clarity will aid the algae’s photosynthesis and it wont take very long for the bloom to reappear.

The most efficient solution is to use a UV light and filter. There are also a wide range of chemicals available which work in a number of ways, some killing the algae, some hindering its growth. There isn’t a chemical remedy which will work for every pond, so it can be a bit of trial and error finding the best solution for a specific pond.There are some filtration methods, such as the use of magnets set along the pipe-work, and multi frequency processor units, which are available as treatments for both suspended algae and blanketweed. However these treatments are sometimes criticised for the lack of impact they have and while they may help to control the build up of algae, they don’t seem to fully get rid of the problem.