Aquatic algae, (thought of by many as pond scum) are microscopic plants that grow in sunlit water that contains phosphates, nitrates, and other nutrients.  Algae, like all aquatic plants, add oxygen to the water and are important in the fish food chain. They share many characteristics with plants, although they lack true stems, roots, and do not flower.  Common algae that forms in ponds include planktonic algae (green water algae) and filamentous algae (string algae).

Algae is actually important and beneficial to a pond or water garden.  It is part of the eco-system we want to establish in the ponds because it helps in maintaining good water quality.  If the pond filtration and circulation system are properly designed, the nutrients and toxins can be controlled, there by controlling algae growth.  The perceived algae problem begins when algae grow in abundance, but this condition is really a symptom or an indicator of excessive nutrients and or toxins in the pond water.

Excess nutrients are typically caused from feeding the fish too much, too often, or both. In addition, leaves, grass, or other organic material find their way into the pond, settle to the bottom and begin decaying and releasing nutrients into the water.

Excess toxins are typically generated directly from fish and decomposing matter. When fish breath they release ammonia into the water form their gills.  If the pond is overstocked, either by too many fish or too large of fish, you may find the water looks like pea soup. In addition, decomposing organic material such as fish waste, leaves, sticks, grass, etc., can generate toxins.

As a general rule, if you are experiencing an algae problem, adding more of the ‘right kind’ of filtration will help you reduce and manage the amount of algae in your pond.

This includes:

  1. Plants, such as lilies, shade the pond and reduce the amount of sunlight available for algae growth.
  2. Fish, especially koi, will eat a tremendous amount of algae.
  3. Rocks and gravel provide surface areas for bacteria to colonize in and between the rocks, which is like having an additional biological filter in the pond.
  4. Skimmers act as a mechanical filter by removing leaves and other debris from the surface of the pond before they can sink to the bottom and decompose and then turn into either nutrients or toxins.
  5. Biological Filters provide an area for bacteria and enzymes to colonize which consume nutrients and help break down organic debris and fish waste that would otherwise contribute to water quality problems.

Algae is a part of nature just like the other parts of the eco-system.  The main goal in keeping clean water is not to attempt to completely rid your pond of algae, but to keep it in balance with nature.

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