Keeping ponds freshwater clean

Flower & Garden Magazine, April-May, 1996 by Robin Pendergast

A Pond's Cool, Calm Surface mirrors the simple beauty of nearby flowers and shrubbery, making it a natural focal point in any garden setting. So it's not surprising that small, freshwater ponds are a popular feature in home gardens and rural landscapes.

Today's ponds have multiple uses beyond simply being pretty -- everything from irrigating a nearby garden to raising fish. Large ponds also offer recreational opportunities, including swimming in summer and ice skating in the winter.

While a pond can provide both tranquillity and natural resources, ponds that are improperly maintained can become havens for bacteria and algae, ruining natural landscapes. Therefore, it's important to know how to properly care for a pond.

A natural pond is a depression that is fed by a creek, spring or stream. Over time, topsoil erodes into the depression, making it shallower and slowing the water that moves through it. Slower, shallower water conditions warm pond's temperature, accelerate silt buildup and promote algae growth. If fertilizers are used in the area -- on lawns or nearby farms, for example -- the runoff containing these chemicals will increase the nitrogen levels in the pond water, exacerbating the algae problem. Similarly, constructed pools can suffer from fertilizer runoff and stagnant water.

To keep a pond healthy and increase its life expectancy, continual water flow is needed. Not all ponds or garden pools are located near a spring or brook, however. One of the simplest ways to maintain water movement artificially is through aeration, using surface aerating equipment such as electrical or gas-powered water pumps, or diffusion aerators, which function underwater. Water pumps can be used in conjunction with mechanical or biological filtration systems to remove algae, fish wastes and sediment, providing an additional degree of water clarity.

Surface aerators oxygenate the water by circulating cold water at the bottom of a pond and bringing it to the surface. The water is propelled into the air in a fountainlike spray, a water jet or a splashing or gurgling pattern. Such aeration gives ponds healthy levels of dissolved oxygen, which help a pond to thrive. There is also an aesthetic value to surface aerators. Many of the spray patterns available will enchance or dramatize the look of a pond while adding the soothing sound of splashing water.

Electric-powered pumps provide a continual aeration source. These aerators -- splash, floating or fountain-type -- are highly efficient and help oxygenate water while maintaining temperature levels. For small, self-constructed ponds, a 1/2-to 1-inch fountainhead may be all that's needed to oxygenate the water. Most small water ponds, which hold between 50 to 2,000 gallons of water, can easily be aerated with a fountainhead that retails for about $25 to $30. Some steel-molded fountainheads retail for about $75. Alternatively, water from the pump can be oxygenated by directing it into a waterfall that cascades over rocks and back into the pond.

In choosing an aerator for a larger pond, consider the aerator's horsepower. A good rule to keep in mind is one horsepower per 1.5 surface acres of pond. Prices depend on the type of aerator as well; as horsepower. A floating, motor-only-aerator costs between $415 and $560. A small fountain-type aerator may run from $355 to $550, with a large fountain-type running from $1,500 to $3,000. Splash-type aerators are priced between $440 and $500.

Gas-powered pumps can also aerate water to help improve pond water quality. These types of pumps are convenient and versatile and many times are used for emergency aeration. For example, if fish are dying because outdoor temperatures are hot and the level of dissolved oxygen drops, a gas-powered pump can be used to even out water temperatures and keep fish healthy. Since no electricity is involved, this type of pump is safe to operate while swimming.

Gas-powered pumps are also mobile and can be used to irrigate lawns and gardens. High-quality pumps make irrigation easy, pumping more than 1,600 gallons of water per hour. During the winter months, gas-powered water pumps can be used to resurface skating ponds. A high-quality, gas-powered water pump retails at around $320.

Diffusion aerators, such as compressors or blowers, oxygenate water from below the surface without any electrical hookup underwater. They inject air into a pond with an air hose, which may be electrically hooked up outside the pond. This setup may be preferable if people plan to swim or fish in the pond and there is a concern about a possible short circuit. Diffusion aerators reduce algae without chemicals, aid in circulating pond water and help to decompose sediments.

Sometimes algaecides are recommended to control algae and underwater vegetation, but these chemicals are detrimental to fish and other wildlife. From an environmental standpoint, a more natural method of algae control is preferred. Careful choices of landscaping material around a pond -- stones, shrubs, groundcovers or sod -- limit the amount of surface runoff entering the pond. When combined with a filter and an aerator, this technique can extend a pond's life. If the pond is small enough, pond liners may also improve water quality.