One of the biggest challenges facing pond owners is green water. This occurs when minute forms of water life such as algae get out of control and start taking over the pond. These can include mixtures of both free floating and suspended species such as blanket weed, silkweed and mermaids hair. Algae can quickly choke up garden ponds and create an unattractive ‘pea soup' appearance.
Is green water caused by an unhealthy pond?
Many people think green water is a sign of an unhealthy pond. However green water can affect all types of ponds and is common in those that are rich in nutrients. Even well balanced ponds can suffer from green water and this is common in spring. At the beginning of the growing season a temporary film of algae can bloom on ponds as the water starts to warm up. This is not a cause for concern as typically once the other aquatic plants start to grow the algae bloom will disappear again.
Common Problem Species
There are some more persistent forms of water life though that will need to be treated. Blanket weed in particular can form a very thick mat-like growth across ponds which can be difficult to remove. This can block light from the pond causing submerged plants to die. Silkweed can also be a troublesome addition to ponds and will tangle around water lilies and submerged plants ruining the visual look of ponds. Silkweed can be removed by hand but it is very slippery and this can be a frustrating and time consuming job.
Biological treatments can offer some success when treating green water. With biological treatments pond owners aim to create a natural balance that will discourage algae from spreading prolifically. This includes two main techniques:
Submerged Plants - by creating a sufficient level of submerged aquatic plants pond owners can ensure that spare plant foods available in the water are used up. This will discourage algae from forming as there will be few spare nutrients for it to feed from.
Surface Shade – natural surface shade from water lilies and other floating foliage can reduce the light falling beneath the water and discourage algae from growing.
Marine Life – certain species of marine life such as ramshorn snails and fresh water muscles can act as natural algae filters. They cannot clear a green water pond alone but will help to maintain a natural balance.
For serious green water problems sometimes chemicals are the only solution. Algicides can clear green water quickly and can help to prevent it from returning before a more natural balance of plants can be achieved. There are two main types of algicide:
Potassium Permanganate – products with this chemical base are used for suspended algae problems and green water. This can only be used when the water is cool otherwise it can damage marine life and turn the water a yellowish colour.
Copper Sulphate – products with this chemical base are effective against both filamentous and suspended algae but only very minute concentrations are safe to use if you have marine life such as fish and molluscs.