Sept. 1 2006 12:00 AM

7_4.jpgLets face it: an algae-infested pond isnt a pretty site. Algae can make a beautiful water garden look like a pool of slime left over from a Halloween display. They also complicate the maintenance of a pondalgae can clog filters and equipment, ruin wood, and suffocate plants and fish. Some species of algae double their population as often as every twenty minutes. But not only are they quick to reproduce, theyre also stubborn. How can you get rid of them?

First, you need to remember that algae are plants. Like any plant, they need three elements to survivelight, water, and nutrients. Take away any one of these necessities, and algae are controllable. Naturally, you cant take away water. But light and nutrients are different matters entirely.

At first, the thought that you can control the amount of light reaching a pond sounds absurdtrees or buildings may provide a certain amount of shade, but beyond that, its not like you can turn off the sun! However, floating plants are a greatand aestheticway of controlling the amount of light a pond receives.

Plants like water hyacinth, water lettuce, and water lilies are widely available and will eagerly reproduce to cover the waters surface. Some experts suggest that plants with floating leaves should cover up to 50 to 75 percent of a pond.

Mike McGee, president of EP Aeration, San Louis Obispo, California, says that, The key in algae control is nutrient control. Angela Hopko, marketing manager for Otterbine Barebo, Inc., agrees: Theres a direct correlation in the level of available nutrients and the populations of algae.

Nutrient control starts even before a pond is built. Ponds should be designed so that water running off the landscape doesnt run into them. The organic debris, fertilizers, and yard chemicals present in runoff are all considered tasty snacks by algae invadersyou might as well set out an algae buffet.

Nutrient loading can be very high in waters adjacent to green areas or turfgrass, Hopko warns. If a pond is already constructed, some kind of barrier can be placed around the edge to stop the flow of runoff.

Overstocking a pond with fish and overfeeding fish can also give rise to algal blooms. Fish waste and leftover food are perfect nutrients for algae to feed on.

Adequate filtration is another important step towards limiting algae propagationwhatever material the filter removes is not feeding algae. I tell contractors that algae problems in a clients pond can almost always be traced back to too many fish, too heavy feeding, and inadequate filtration, says Carolyn Weise, consumer relations manager for Ecological Laboratories, Freeport, New York.

Submerged plants can also help. They feed off the nutrients in the pond water before algae get a chance. If the nutrients in a pond can be consumed at the same rate as theyre being introduced, you can pretty much solve an algae problem, McGee says. Some companies make products for aerating ponds by introducing air and oxygen at their deepest level. Getting oxygen to this oxygen-depleted area can be critical in the fight against algae.


Oxygen works via a chemical reaction to sequester nutrients at the bottom of the pond, where they cant be used as food by algae, McGee explains. Many of the most common nutrients found in ponds become insoluble in oxygen-rich water. Being insoluble makes them heavy, and they sink to the bottom. Algae like to stay near the surface, where sunlight is readily available, and cant follow the nutrients down.

Proper oxygenation of water can also aid aerobic digestion of nutrients and sludge. Aerobic organisms consume nutrients, but can only survive when oxygen is present. Also referred to as microbes, aerobic organisms are another big element of algae control. Aerobic bacteria feed on nutrients and digest them into compounds that algae cant use for food, Hopko explains. Many manufacturers make products that contain microbes for this precise purpose. This is a great approach to managing algae, because its organic; it doesnt require chemicals, says Casey Coke of Natural Environmental Systems, Dallas, Texas.

I would highly recommend regular use of a microbial product to maintain a stable ecosystem to any landscape contractor managing a pond, says Weise. She also advises not to wait until an algae problem has started before using these products. By the time the problem arises, the cure can be worse than the problem, she says.

A first thought to fight algae would be to go for an algaecide. However, while these products can eliminate both planktonic and filamentous algae, some are not safe for ponds with fish and aquatic plants, and should only be used in decorative ponds and fountains.

Additionally, algaecides can sometimes work too wellif a product kills algae too quickly, it can deplete the oxygen in a pond, or worse, the dead algae can feed a whole new crop of algae, and the problem begins anew. This is another benefit to the organic approach, says Coke. It works at a slower pace.

But if your algae problem is already significant, you may not have a choice but to use an algaecide. You can kill the algae you already have, then start with a clean slate and begin fighting algae using other techniques. Some manufacturers offer products that combine algaecides to kill the algae with microbial products to consume the dead algae. Its vital that contractors understand the importance of good pond care and regular husbandry using microbes to prevent algae problems, Weise says. With knowledge like this in your back pocket, it should be easy to keep water gardens crystal-clear and algae-free.