It is not unusual to have a little Algae growing in garden ponds, in fact small amounts can be beneficial to pond life. Large amounts however can be not only unsightly but also detrimental to the health of the pond.
A number of factors can cause the growth of green algae in ponds, its removal is not difficult in smaller pond however it is basic pond design that can help control or even prevent the problem in the first place.
Algae thrives on dissolved nutrients in the water and sunlight, excess nutrients from fertiliser run off into a pond, over feeding fish, and decomposing plants can all add to the algae problem in a pond. Now not all algae is bad, a little is expected in most ponds, however large amounts cause problems, it uses up oxygen and this is a real problem if you have fish, and a pond covered in a layer of green does not look that great.
Factors that cause Algae.
- High light levels combined with other factors are a major cause. The light encourages algae growth,it also warms the water, which also speeds up growth.
- Excess runoff of fertilisers will add to the problem. Excess feeding of fish can also be a problem.
- Poor water circulation is a third factor.
Control of Algae in Ponds
Prevention is better than cure and poor pond design can be a major cause of green algae. A pond needs to designed so that accumulated waste from dead plants, fallen leaves etc can easily be removed. This can be achieved by having the pond slope to one or two deeper sections that are easily reached with a scoop so that the waste and rotting material can easily be removed without emptying the pond. You can install a skimmer (similar to this on a swimming pool) that will remove debris before it sinks.
Use a pond liner, concrete tends to encourage algae growth. And most importantly install a pond pump that will move adequate quantities of water. Connect this to a water fall or a fountain to increase the amount of oxygen in the water and this water flow can help prevent growth.
Provide some shade, this cools the water. A well located tree is excellent, as long as it does not drop to much litter into the pond. Water lilies with their large leaves provide excellent protection from the sun and help keep water cool.
The simplest way to remove algae is to flush the pond, as long as the water used does not contain nutrients such as phosphorus. This is really a short term solution and you need consider the prevention techniques.
You can use chemicals to control the algae, however this is really only a temporary measure. You would also need to clean out the dead matter after treatment as this would act as ‘fuel’ for the next bloom.
- A pond vacuum or scoop can remove accumulated debris and rotted matter from the bottom of the pond.
- Pond plants are essential as they tie up nitrates that cause the algae blooms.
- Some protection from direct sunlight, especially in the afternoon can also help reduce pond algae.
- Oxygenate the water using a pond pump and fountain, or a water fall.