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Pond Construction Considerations Pond Siting Site selection is critical to the ultimate success of a garden pond. Several factors should be considered: 1. The location should receive at least six hours of direct sunlight every day, and an additional six to eight hours of indirect light is desirable. Many of the common species of plants kept by pond hobbyists have high light demands, but too much direct light will lead to problems with overheating and troublesome algae. 2. The site should be reasonably free of overhanging trees and plants. Falling leaves and pine needles can cause problems as they accumulate and decompose within the pond. Employing catch netting and frequent skimming will help alleviate this problem. 3.
The area around the site should have excellent drainage characteristics
and should not be located too close to easily flooded basements
or buildings. Pond overflow from excess rain/snow needs a place
to dissipate. It is also important to ensure that the location is
not a catch basin for runoff from a driveway or lawn. Runoff water
could contain pesticides, fertilizers, road salts or other chemicals
that would be detrimental to your pond.
4. The pond should be located near a source of tap water. "Topping
off" and water exchanges will be much simpler if the pond can
be reached with a garden hose. Most ponds will benefit from some
sort of filtration, or at least supplemental aeration, either of
which will require electricity. It is simplest to utilize an outlet
installed on the side of a house or in a garage or basement window.
Many of these requirements may be modified without detracting from the beauty of the pond. For example, if you do not wish to grow water lilies or other plants requiring high levels of light, ferns and other varieties of low light plants could be supported in a shaded area. As a beginner, it would be wisest to attempt to satisfy as many of the above guidelines as possible. Pond Size, Depth, Shape Size: Ponds can range from one hundred gallons to thousands of gallons in size, or even be supported in a 50-gallon tub on your deck. The most important consideration with regard to size is the temperature and chemical stability of the pond. The larger the body of water the more stable the water chemistry and temperature profile, because changes in pH and temperature occur much more slowly in large volumes of water. So what exactly is the best starting size for a pond? The answer to this question is determined mostly by personal preference. Many people are successful with ponds of just a couple hundred gallons. However, if your goal is to keep many species of plants, and some of the larger fish, such as koi, the pond should hold as least five hundred gallons of water. The average size for a pond installation in this area tends to be around one thousand gallons. This may seem to be an enormous volume, but once installed, the scale will seem different.
The easiest way to estimate the size of a pond is For example, if a rectangular pond is 150 inches long, 80 inches wide and the water is 24 inches deep, the number of gallons would be 150 x 80 x 24 x 0.004329 = 1,247 gallons Since most ponds will be irregularly shaped, it is wise to compute size in sections. Liners: Pond liners come in many varieties. There are prefabricated plastic pools available in a variety of shapes and sizes, but most ponds are designed utilizing a flexible liner made of PVC or some other soft material. These types of liners allow the most flexibility with regard to size, shape and depth. Of the flexible materials available, butyl rubber is the most suitable. Although initially more expensive than PVC liners, butyl does not degrade under ultraviolet light and will last approximately 40 years. Most butyl liners are around 3 mils in thickness, whereas PVC will usually come in 20 or 32 mil thickness. If you choose PVC make sure that it is fish grade. Some liners intended for swimming pool use are coated to retard algae growth and will be toxic to plants and fish. Depth: The minimum depth for any pond in the New England climate should be 18 inches. Ideally the pond should have a center step down to 24 to 30 inches. This provides a place for "overwintering" fish and plants to seek refuge during a hard freeze, because a pond this deep will not freeze solid. Pond Maintenance Considerations One of the largest problems that the pond hobbyist must face is green water, or the overabundance of free-floating algae. Algae can be found any naturally existing body of water. Why, then, are some ponds clear and others a murky green? It boils down to one word--balance. In order to have a clear pond where fish and plants can be easily viewed there must be an overall balance between the natural cycles occurring within the pond itself. The decomposition of plant materials from internal and external source coupled with fish wasters and the addition of fertilizers and other organic inputs leads to the formation of nutrient soup in the pond. Ammonia from fish waste products and decomposing organic material can be toxic to fish, but natural processes in the water can minimize their harmfulness. One type of bacteria turns ammonia into less harmful nitrite, which is, in turn, transformed by another type of bacteria into even less harmful nitrate. Nitrate is one of the primary ingredients necessary to fuel the growth of water clouding algae. So in a small body of water, such as a garden pond with a high load of plants and fish, it is easy for the water to become loaded with nitrate. Although there are natural cycles to the removal of nitrate, the average pond is too high in organic load for these cycles to be sufficient. Together, nitrate and phosphate, the other naturally occurring primary plant nutrient, cause green water in many garden ponds. There are several ways to correct the problem of murky water. Most of the effective solutions involve the utilization of some form of external filtration technology. Although it is possible to balance a pond naturally with a high percentage of plants and very few fish, most water gardeners opt to stock fish in higher densities as an aesthetic preference. A water gardener might often spend the entire growing season attempting to balance that tiny patch of water in the yard only to be disappointed by failure or the onset of winter. For most, some kind of filtration technology makes the most sense. Filtration methods can be used alone or in combination with each other for greater effectiveness. Mechanical Filtration--Mechanical filtration involves the physical removal or trapping of particles on some sort of fibrous or particulate medium. This is usually accomplished by pumping water over some sort of brushes or sponge-like foam. Mechanical filtration allows materials to be removed from the pond before they decompose. To be effective, a mechanical filter should be cleaned at least once a week to limit the breakdown of trapped debris. Biological Filtration--Biological filtration involves the pumping of water over some sort of substrate, allowing the colonization of large numbers of beneficial bacteria that aid in the breakdown of toxic organic compounds and the conversion of ammonia to nitrite in the pond. It is important to employ biological filtration after mechanical filtration to avoid clogging the biological media, permitting the beneficial bacteria to function unimpeded. Bio-media usually consists of perforated foam pads or, more commonly, some sort of plastic balls or shavings with a high surface area. One medium to be avoided is porous lava rock. Although effective, lava rock eventually becomes clogged with organic material that reduces its effectiveness. Sterilization--Ultraviolet sterilizers are pieces of equipment that are frequently used by the most serious water gardeners. These units use ultraviolet light in a sealed module to kill free-floating algae, parasites, bacteria and many other types of harmful microorganisms. Since water is passed through them and returned to the pond, fish and other plants are unaffected. Ultraviolet sterilizers have the ability to clarify a pond overnight, but they should still be used in conjunction with mechanical and biological filtration for greatest efficiency. Without first filtering the water, a sterilizer will become clogged and lose much of its efficiency. Water Changes-- Any one who has ever kept an aquarium will remember periodically changing a portion of the water in the tank. It is important to dilute the accumulation of potentially harmful nutrients and substances within the aquarium. This suggestion cannot be stressed enough when it comes to a garden pond, because there are far higher concentrations of potentially toxic materials in a pond than in the average home aquarium. A partial water change of a least 10-15 % of the pond volume should be performed at least twice annually. Many experience water gardeners change the water in the fall to remove organic material before the onset of over-wintering, and again in the spring after the thaw and the onset of plant growth. Aeration-- Supplemental aeration adds oxygen and removes carbon dioxide from ponds. It is especially beneficial to a heavily stocked pond or in a pond that has been unusually warm during the peak summer months. Aeration is accomplished by stirring the surface of the water in some mechanical manner or using some type of air diffusers or "bubblers." These could include an air pump and air stone(s) like the ones used for aquariums or the utilization of a fountain or waterfall to stimulate movement of the water. Many types of mechanical and biological filters also help to aerate a garden pond. Netting-- Spending just 10 to 15 minutes a week netting fallen leaves and other dead materials from the surface and bottom of your pond can contribute significantly to clean water quality. Used in conjunction with some type of filtration and/or aeration and water changes, netting completes a well-rounded maintenance system. Water Quality Considerations Water quality is a very important aspect of a successful pond endeavor, and the most important aspect of water quality is stability. Changes in physical and chemical attributes should occur slowly over a period of days, not minutes or hours. Drastic changes in water parameters are the largest cause of disease outbreaks and plant and animal mortality. There are several water quality parameters that should be monitored at least on a monthly basis in an established pond, and weekly in a more recently created one. Chlorine: Most municipal water supplies are currently treated with either chlorine or chloramines to sterilize the water for drinking. If you are unsure about your local water, contact your supplier. While not harmful to humans or pets, these chemicals are highly toxic to aquatic plants and animals. Luckily, they are easy to remove. Chlorine will simply dissipate into the atmosphere from a newly filled pond (no plants or animals) if allowed to stand for at least 24-36 hours. Chloramines are more complex chemicals and should be removed with one of the inexpensive commercially available treatments. One must remember to treat with dechlorinator when topping off or changing pond water. Many of these conditioners contain added ingredients to help stabilize water chemistry and eliminate contaminants such as heavy metals. It is wise to always utilize one of these products. Test kits for chlorine are inexpensive and are available at all pet shops and pool centers. pH: The pH is the degree of acidity or alkalinity in your water, and should be checked occasionally. The pH of municipal water supplies may fluctuate due to the periodic addition of buffer solutions. For healthy fish and plants, however, pH should never fluctuae drastically in any pond. The pond itself should be in the range of 6.5 to 7.5, though many fish and plants will tolerate some deviation from this range. After a pond becomes established it will normally fall somewhere in this optimum pH range, but it is not a good idea to test the limits. Extremely acidic water can bee countered through the addition of pure household baking soda (start with one teaspoon per 500 gallons). Extremely alkaline waters can be treated with the addition of household white vinegar (start with 1/4 cup per 500 gallons). Allow at least 12 hours between additions and recheck the pH. pH test kits are also inexpensive and available at most pet stores. Make sure you purchase a wide range kit. Temperature: The temperature of your pond is often in the hands of Mother Nature. An inexpensive floating thermometer intended for aquarium use will suffice. It will also be useful for determining when fish will begin to show reduced activity and food requirements in the fall, as well as begin to feed in the spring. Water temperature will also dictate times for the addition of certain types of aquatic plants. During the hottest days of summer, high temperature may alert the pond keeper of the need for supplemental aeration. Here is a list of significant temperature changes (degrees F) <45 Most hardy plants will die back for winter. Dead leaves should be removed. Fish will remain listless and should not be fed again until the spring warm-up. Over-wintering plants should be moved to deeper water to avoid freezing (approx. 18 inches). Remove as many falling leaves and accumulated leaves from bottom of pond as possible. Winterize filters and move pumps to center of pond, but leave them on for circulation and de-icing. <60 Move tropical plants indoors for over-wintering. With first frost many floating and submerged plants will begin to die back. Discard them before they decompose. >45 Hardy plants can be moved to shallower water for new growth. Fish will be begin to feed and exhibit spawning behavior. A partial water change is recommended. Plants may need to be divided and fertilized. Filters, pumps, etc. should be reconnected and started. >95 Oxygen levels in pond prone to severe depletion. Many hardy lilies will cease to bloom. Green water algae may take over pond. It may be wise to reduce or halt feeding of plants and fish until water temperatures drop back into the 80s to ease the bio-load. Do not worry about starving your fish or plants, they can go indefinitely without supplemental feedings. Although there are other water quality parameters that can, and sometimes should, be monitored, the above parameters offer an excellent starting point. For example, if you are going to keep high densities of large koi, the ammonia and nitrite levels should be monitored to ensure that the biological filter is functioning properly. As mentioned earlier, a garden pond can be an exciting project if some basic guidelines of construction and maintenance are followed. There are many ways to cope with the most common problems faced while building a new pond; what works in one case will not necessarily work in another.
Adapted from Neil D. Marcaccio and Michael A. Rice, 2001
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