October 1, 2014
By Catherine Neville, B.Sc., M.Sc.
Excellent pond water quality and clarity is attainable, it just takes a bit of work. Like anything in life, however, if it is worth doing, it is better if it is done right. There is no quick fix or magic potion when it comes to proper pond maintenance. Instead, it requires an understanding of the five essential elements that contribute to water quality and clarity: circulation, aeration, filtration, beneficial bacteria, and aquatic plants.
A clean pond begins with an annual spring cleanout, which mimics Mother Nature’s spring runoff. The pond is drained with a solids handling cleanout pump and discharge hose, the rocks are pressure washed to remove string algae, and the pond is flushed to eliminate leaves and debris that have accumulated and sunk to the bottom over the course of the year. Once the discharge water runs clear, it is time to refill the pond and fire up the pump.
To achieve lasting water clarity, it is essential to have a filtration system. This typically involves a biological filter/spillway or waterfall unit at one end where cascading water will create fresh oxygen for the pond. The waterfall can also be set back to create a meandering stream that gently flows into the pond. This increases the filtration capacity of the water feature as the stream bed traps debris and the water is cleaned by the beneficial bacteria colonizing in the river wash gravel. Set at the opposite end of the pond, the skimmer protects the circulatory pump and skims the debris from the water’s surface by drawing water across the length of the pond.
Keep in mind, however, water circulation and aeration alone are not sufficient for sustained water clarity and quality. Water filtration is important and can be achieved by ensuring the pond includes some biological media, typically filter pads and other filtration means, which allows beneficial bacteria to colonize. These bacteria clean the water as it passes through the biological filter.
Beneficial bacteria metabolize decaying matter and waste into ammonia, which is converted into nitrite and finally into nitrate, which is essentially fertilizer for the pond plants. Although beneficial bacteria occurs naturally in an ecosystem pond, it is recommended the appropriate amount (based on the pond’s water volume) of commercially prepared beneficial bacteria be added on a weekly basis throughout the water gardening season to allow the bacterial colony to flourish and create positive results.
It is also important not to dismantle or clean the biological filter, regardless of how dirty it appears as this will disrupt the established beneficial bacterial colony. By doing so, it will have an adverse effect on pond water quality rather than improving it.
Pressure filters or canister filters have become a popular alternative to traditional biological filter and skimmer combinations. External pressure filters can be recessed into the ground or hidden behind plants and are paired with a solids-handling pump that can sit at the bottom of the pond, without the need for a skimmer. However, if the pond is located near trees that drop their needles or leaves, then the use of a skimmer is highly recommended.
For smaller ponds where the client does not wish to invest a lot of money into filtration equipment, a Band-Aid alternative is recommended. This involves wrapping the pump with biological filtration media which allows the water to be cleaned by colonies of beneficial bacteria growing on the filtration media before it is circulated through the pond. When paired with various aquatic plants, this can be an effective and low-cost method to improving water quality and clarity.
When selecting a pump, it is important to choose one that is appropriately sized to the pond to ensure it will circulate the entire water volume at least once per hour. For ponds less than 3785 L (1000 gal), the recommended turnover rate is increased to one and a half to two times per hour as smaller ponds are harder to keep clean than larger ponds. The latter are better able to metabolize change than smaller ponds which are more sensitive.
In the absence of a skimmer, choose a solids handling pump that is engineered to sit on the pond floor. Be sure to account for friction loss associated with the length, diameter, and type of tubing used, as well as the measured head height, which is the distance between the surface of the water and its point of origin, e.g. a spillway or an outlet from a pressure filter.
If the pond is 11356 L (3000 gal), a pump rated for 190 litres per minute (lpm) (50 gallons per minute [gpm] cannot be used. Friction loss and head height calculations must be considered; therefore, a pump with an output of at least 250 lpm (66 gpm) would be recommended. It should also be considered that the pump will need to operate 24-7—from as early as possible in the spring until the pond water is at risk of freezing.
The importance of plants in a pond cannot be over-emphasized as they are nature’s filter. Plants are an integral part of a properly built pond’s filtration system. A pond should be constructed using shelves to allow marginal plants to be installed along the edges and a deeper 0.6- to 0.7-m (2- to 2.5-ft) shelf to accommodate lilies. It is recommended that lilies cover a quarter of the pond’s surface area, while floating oxygenators, such as water lettuce and hyacinths cover an additional quarter.
The long roots of the floating oxygenators are not only superb at absorbing nutrients from the water, but they also filter silt and debris. Submerged oxygenators, such as hornwort or parrot’s feather, release oxygen into the water and trap debris against their fronds.
The most common complaints from pond owners are to do with the waterfall and rocks being covered with string algae—a filamentous plant that elongates by adding cells end-to-end like boxcars—or their water looks like pea soup, which is caused by a single-celled algae (commonly referred to as suspended algae). Both algae types can be caused by an excess of nutrients in the pond. Likely sources include waste from too many fish, runoff from lawn fertilizers, over-exposure to sunlight, or even from alkaline rock, such as limestone, rather than chemically-inert granite, which is recommended for pond construction. In fact, limestone will increase the pH of the pond water, creating favourable conditions for rapid algae growth.
These two types of algae sometimes confuse pond owners as the presence of string algae can create the illusion of the water being green. The true test in determining the presence of suspended algae is to hold a glass of pond water up against white paper; if the water appears green there is a suspended algae problem.
An effective way to eliminate suspended algae is to install an ultraviolet (UV) clarifier/sterilizer in-line with the plumbing. As pond water flows past the UV bulb, the algae cells are destroyed by the UV light. In the absence of this technology, it is more difficult to eliminate suspended algae from a pond.
Beneficial bacteria should be added every day for at least two weeks and fine filter pads should be inserted in front of the existing skimmer filter mat to trap and digest single-celled algae. As part of this process, the filter pads should be cleaned every day until the water becomes clear.
String algae is not harmful to the pond’s ecosystem, however, it is a sign the pond’s nitrification cycle is working well. In gardening terms, the string algae plant is to water gardening as the dandelion is to turf.
Embrace the algae, if possible, and let koi feed from it, however, if the tolerance level has reached its limit, string algae can be eliminated with the use of an electronic clarifier as long as the pond’s water chemistry falls within the correct parameters. This clarifier works to eliminate string algae by introducing copper ions into the water. Copper binds to and interferes with the algae cell’s ability to absorb nutrients, causing the plant to die. Alternatively, an algae treatment product can be used to control or remove the algae from the rock by binding the available calcium it requires for adhesion.
With the algae removed from the rock, it needs to be digested and removed by a bacterial/enzymatic product. If the algae or other debris accumulates at the bottom of the pond, it can be digested with a liquid sludge cleaner or by using pure strains of concentrated beneficial bacteria, including enzymes. Liquid barley extract or barley pellets may be used to prevent future algae blooms, or at least reduce their impact by releasing naturally occurring peroxide into the water. This interferes with the elongation of the string algae cells, drastically reducing their growth.
Another algae prevention method often used by mini-putt courses is the addition of natural or blue pond dyes to the water. The dye forms a protective layer on the surface of the pond, which prevents sunlight from reaching the algae cells, interfering with the vital process of photosynthesis.
Other common complaints include murky water, which is usually caused by rainstorm runoff or pollens dropping into the water. In either of these cases, a flocculent can be used to bind the particles together to trap them on the filter pads within the skimmer. Pollen can also cause the formation of foam, particularly around the waterfall. When pond fish are spawning, one usually observes the presence of foam created by the abundance of excess proteins in the water released by the male fish, which are agitated by the rapid movement of the pond’s waterfall. In this case, an anti-foam product can be used or simply let nature take its course.
In the fall, if a net is not placed over the pond, leaves will accumulate and sink to the bottom where they will release tannins (a byproduct of their decomposition). Activated carbon may be used to absorb the discolouration in the water, which also has the side benefit of neutralizing foul odours. Care must be taken by pond owners who use an electronic clarifier to control string algae as the activated carbon will also absorb the released copper ions.
Clients who invest in their ponds in early spring will save money with regards to water quality management throughout the remainder of the season. For example, clients who buy one or two floating plants (when their pond should contain at least a dozen) thinking they will multiply in time to provide proper shade for the pond and absorb the excess pond nutrients, are deluding themselves.
It is important to start off with proper plant coverage—even if it means discarding their progeny later—so the pond can get ahead of the algae blooms, or possibly prevent them altogether. Keep in mind, it is easier to work with Mother Nature than against her.
Catherine Neville is the owner and general manager of The Pond Clinic Water Garden Centre, located in Nepean, Ont. She holds a bachelor of science in life sciences from Queen’s University and a master of science in molecular genetics from the University of Ottawa. A self-taught businesswoman, Neville applies her scientific precision to every aspect of her second career as a garden centre retailer, which she and her husband, Nicholas Bott, established in 2007. She can be reached via e-mail at email@example.com.
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