Every pond and water garden is home to numerous species of plants and animals, including algae. When kept in check, algae aids in the processing of nutrients called the "nitrogen cycle." However, with abundant nutrients and sunlight, algae is quick to take over a pond creating green water and long strands of slime that wrap around aquatic life. Aquatic animals are the first to feel the effects of algae problems, with aquatic plants coming second if the problem is not remedied in a timely manner.
Ornamental pond and water gardeners will generally encounter three types of algae: single-celled (planktonic), multiple celled, and elaborate plant bodies (filamentous) also known as pond scum. Single-celled algae organisms float free in the water and typically turn the water green. Multiple celled algae organisms can float free but are more often found adhering to hard surfaces in the water, creating a fine moss-like covering. Filamentous algae grows in long strands of green slime that adhere to hard surfaces and entangle aquatic life.
An overabundance of algae causes many problems with pond health beyond aesthetics. Oxygen depletion is a main concern; a sudden blossom of algae depletes the water of oxygen and leaves aquatic life struggling to survive. Blockage of sunlight is another issue as suspended algae prevents the sun's rays from reaching the floor of the pond. With no sunlight, water temperature may also drop causing an inhospitable environment for life to survive. Finally, filamentous algae has the potential to wrap around aquatic plants strangling them to death.
Algae plays two very important roles in a process called the "nitrogen cycle." First, plankton algae is a basic food source for zooplankton, microscopic organisms that feed small fish. These small fish either feed big fish or release ammonia into the water from their waste. Fish waste eventually turns into nitrate, a fertilizer for aquatic plants. Secondly, algae changes atmospheric nitrogen into ammonia in the pond. The ammonia fuels the nitrogen cycle and again creates fertilizer for aquatic plants.
While the existence of algae is present in all pond ecosystems, only excessive amounts of it has dangerous effects. Algae blooms occur when a set of conditions is optimal for rapid reproduction of algae cells. Heat, sunlight, and oxygen are the most important factors with excessive nutrients exacerbating the problem. Pond ammonia from fish waste and decaying food as well as phosphorus and nitrogen from fertilizer run-off are water quality factors that create excessive nutrients for blossoming of algae.
Algae problems are hard to resolve. The existence of many commercial products claim to sink algae to the pond floor where it can be vacuumed. However, the most successful method to remedy an algae problem is to add a UV sterilizer to kill suspended algae and physically remove string algae by hand. Bentonite clay and barley straw may also help to rid the pond of suspended algae. Once the problem is under control, preventative measures should be taken.
The best method for resolving excessive algae problems is to prevent them in the first place.Too many fish and unused fish food are major components of ammonia problems as is fertilizer and pesticide run-off. Sunlight can be decreased by adding floating plants and shading the surface of the pond. The presence of aquatic plants keeps algae in check by competing for nutrients. Last, ensure the filtration system is large enough to support the pond and is kept clean.