Green Pool

Frequently Asked Questions

Help! My pond has gone green

Why?

Green water is a natural process due to free-floating cells of algae growing on the nutrients in the water. It is not usually harmful to fish or wildlife. Green water is not necessarily unhealthy, just as apparently clear water is not always safe. Indeed, fish tend to have brighter colouration when kept in green water.

Green water is to be expected in new ponds which tend to have higher levels of dissolved nutrients due to the minerals in fresh tap water and nutrients from planting soil. Usually the green will fade of its own accord after a few weeks or months, as the plants and pond wildlife establishes and a balance is achieved. It might only return as a slight haze for a few weeks at the beginning of each season.

Persistent Green

Green water can be a more persistent problem in shallow ponds; those pools exposed to continuous sunlight; and pools where nutrients are washing in from surrounding soil. It will also occur if larger fish are constantly stirring the pool base or disrupting the plants and balance of wildlife.

Treatments

Although green water can be treated with algicide and flocculating chemicals these are short term solutions and can have side effects, especially if used without accompanying filtration. If green algae dies back all at once, it can pollute the water and use up valuable oxygen. Changing all the water will give only temporary relief, and the newly added minerals could encourage the pond to go green again in a short time.

Longer term

An efficient biological filter will often clear the pool of algae at the same time as improving the water quality for fish. Where green water is more likely a UV unit (glossary) will reliably control pea-soup algae without the need for any chemicals. Ideally UV and biological filters are used together, though UV may be used on its own in certain circumstances. © www.aquapic.com

My UV unit has stopped controlling green water?

If a previously well-functioning UV unit stops controlling green water, despite water flowing through it at the correct rate, it usually indicates that either the internal sleeves have become dirty, and are stopping the light from penetrating the water, or the lamp needs to be changed. UV lamps normally require changing once per year, a job best carried out in the spring.