of Rhode Island GreenShare Factsheets
A garden pond can be a beautiful and exciting addition to any
urban or suburban landscape. Although the construction of
a garden pond may seem to be an enormous task, a little prior
planning and homework should make your project an enjoyable
success. This fact sheet, while not to be considered a comprehensive
or elaborate guide for pond construction, is intended to
help the beginning hobbyist avoid many of the most common
pitfalls in the initial stages of planning, siting, material
selection, maintenance and water quality considerations.
Planning these elements beforehand can help assure the success
of a new pond venture. If you are considering an elaborate
water garden with many fish and complicated design elements,
you may want to then purchase a detailed text with a more
comprehensive treatment of this material. But the key objective
should be to enjoy yourself! Building a garden pond should
be an exciting and rewarding experience.
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
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
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
Length in inches x width in inches x depth in inches x 0.004329
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
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.
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
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
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
<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
<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
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
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program