Algae are the "weeds" of the water garden. Whether the problem is pea-soup colored water, thick carpets of green hair, or floating gobs of olive-drab slime, algae are as unsightly and aggravating as their terrestrial counterparts. Wherever there is standing water, light, warmth and nutrients, algae will soon gain a foothold. Fortunately, though a small amount of algae is nearly unavoidable, there are things the pondkeeper can do to keep them under control.
Plants - if we tilled, fertilized and watered a 10 by 20 foot plot in the backyard, but only planted 3 begonias in it, it would surprise no one that the other 197 square feet would quickly produce a bumper crop of crabgrass, dandelions and thistles. It should be no shock, then, that a similar sized pond with plenty of fish waste or windblown debris but only a handful of pond plants will likewise be overtaken by algae. Pond plants are by far the best means of controlling algae, as they reduce three of the four algae stimulants by shading and cooling the pond, and competing for nutrients. Submerged "aerating" plants and floating plants like water hyacinth, water lettuce and parrot's feather are particularly useful, followed by water lilies, and even marginals. A "balanced" pond contains plenty of plants to consume the waste produced by the fish and other debris. Many pond books recommend covering up to one-half, or even two-thirds, of the surface of the pond with plants.
Circulation/Aeration - Many forms of algae grow fastest in stagnant areas, especially in the warm shallows around the margins of the pond. Good circulation from a water pump or aerator helps keep water flowing and evens the temperature throughout the pond. Aeration from fountains and waterfalls help oxygenate the water and drive out excess carbon dioxide.
Mechanical Filtration - while it's not practical to make a filter large enough to collect all the algae a pond produces, a filter (the larger the better) can help remove fish waste and other debris that serves as a nutrient source for algae. They can also be used to directly filter out "green water" type algae.
Bio-Filtration - while their primary function is to produce healthy water conditions for fish, bio-filters also reduce waste buildup both mechanically and biologically. As the end product of the biological break down process (nitrate) can used as a nutrient by both plants and algae, bio-filters are best used along with a healthy portion of pond plants.
Algae Eaters - tadpoles readily eat most hair algae, and are no threat to other plants. Plecostomus and other algae-eating tropical fish can be kept outdoors during the warmer months, and eat their share of algae as well.
Water Cleaning Equipment - skimmer nets and vacuum/water change devices help remove debris and waste before it becomes "Algae Chow"
Ultraviolet Sterilizers - the high-tech cure for "green water", ultraviolet sterilizers are particularly useful in ponds housing large numbers of koi, which consume or otherwise destroy most pond plants.
Water Treatments for Cleaner, Clearer Ponds
The Newest, and Maybe Oldest, Technique - barley straw, from the plant used to make Scotch whiskey, is being used by pondkeepers for clearer, cleaner water. How this technique works is unclear, but as the straw decomposes it appears to either release something or encourage the growth of something that causes the water to become cleaner-looking and clearer. It also appears that the straw must be placed in flowing, aerated water (near a pump outlet, for example) and the pond surface must not be covered with blanketweed for the proper effect. Please note: Barley straw is not registered with the US Environmental Protection Agency as a pesticide, and therefore no claims are made regarding it's use in preventing, removing, controlling or eliminating algae. This is an all-natural product, and does not contain any known pesticides, chemical additives, or even "ingredients" - it's just straw, already.
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