"Ponds present unique filtration requirements that are easily
solved once you understand the basics"
Gardeners spend their winter months poring through seed catalogs in anticipation
of spring. This is part of the fun of gardening. For pondkeepers, winter
is also a time for planning. That is why we are presenting this two-part
series on pond filtration in the middle of winter. Pond filtration is too
important and costly an endeavor to be approached in a haphazard manner.
If you are thinking about building a pond or improving an existing pond,
now is the time to plan and prepare for that day in spring when you will
actually begin your project.
These letters, like most of the inquiries about ponds I receive through
Aquarium Fish Magazine, on Fishnet and elsewhere, ultimately boil
down to questions of pond filtration. Most ornamental fish ponds - just
like conventional home aquariums - are 100-percent recirculating systems:
the same water remains in the pond all the time unless some special effort
is made to change it. The levels of biological pollutants in the water
rise quickly unless the pond is in ecological balance or a supplementary
filtration system is used to slow the rate of decline in water quality.
LETTERS
Dear Steve, I have a 1200-gallon pond. There are 42 koi living in it,
with an average length of about 10 inches. The pond has been operating
for three weeks without any problems, but now my fish are suddenly dying.
Many are gasping at the surface with their gills flared out, others have
frayed fins and open sores. I cannot figure out the problem. My pond does
not have a filter, but I do change 10 percent of the water every week. John
Ritchie, Massachusetts
Dear Steve, My pond is about 400 gallons in size. I keep just three
oranda goldfish in it, and all appear perfectly healthy, whenever I can
see them that is. My problem is I rarely see the fish because the water
is pea soup green from May through September. I have two waterlilies, some
parrots feather and some cattails growing in containers in the pond. Is
there any way to keep the water clear without using algicides? Maryann Plamer,
Virginia
Dear Steve, I am hoping to breed koi and just installed a 5000-gallon
concrete pond for that purpose. I notice, however, that all the books on
koi say it is necessary to have a pond filter system. Is this true? What
kind of filter is needed? Bert Mulligan, California
When setting up a home aquarium, you can easily purchase simple, effective
mechanical, chemical and biological filtration systems that do a good job
of maintaining water quality. Even the first-time hobbyist recognizes the
need for some aquarium filtration, and store shelves are loaded with an
amazing variety of filters and accessories.
In contrast, filtration is almost always an after thought for the budding
pond enthusiast. The pond is built, fish and plants are dumped in and the
pond is done. Things are usually fine for a while - longer than with standard
aquariums because there is much more water involved. Eventually, however,
water quality-related problems usually do arise.
Part of the trouble is that many first-time pondkeepers are initially
hooked by the idea of having their own miniature version of a "natural
pond." The notion of creating an ecologically balanced system of fish,
plants and insects is indeed attractive, and there are many fine examples
where it actually does work. All too often, however, natural pond enthusiasts
quickly violate the rules of ecological balance by stocking their ponds
with quantities of fish out of all proportion to a properly balanced ratio.
Or, a pond that was initially in balance with many small, young fish is
knocked out of balance within a few years as the fish grow rapidly to maturity.
For example, it might seem reasonable to stock a small pond with several
one-year-old koi. A typical year-old koi could weigh 40 grams (1.4 ounces)
or so. This same fish could weigh more than 400 grams (14 ounces) by the
time it is three years old. Therefore, even if the number of fish in the
pond remains the same, the total fish load in the pond will increase 10-fold
within several years.
When a pondkeeper inquires about filters, he or she learns that the assortment
of commercial mechanical, chemical and biological filter systems readily
available to aquarists has no counterpart in the world of ponds. While
there are several so-called "complete" pond filtration systems
available for purchase, they vary significantly in their practical value,
effectiveness and price. To wisely choose among them, you need to know
a considerable amount about filtration principles and techniques. Some
pondkeepers, frustrated by the lack of commercially available filtration
systems to choose from, realize that they might be better off attempting
to design and build their own pond filter. It is certainly less expensive
and almost always more effective when tailored to a particular pond.
This article looks at the fundamentals of pond filtration, with an emphasis
on practical design and operation. More than 20 years of research and experience
by fisheries scientists, aquaculturalists and waste water treatment specialists
has produced a substantial body of findings that is directly relevant to
the filtration of ornamental ponds. There are many possible filter designs
that adhere to these principles. I really don't believe that there is any
single optimum filter system design - although some may be better than others
in terms of operation and maintenance. Consequently, this article steers
clear of proposing a particular design. (Those who are interested in construction
details of different designs should consult KOI USA, the magazine
of the Associated Koi Clubs of America (P.O.Box 1, Midway City, CA 92655).
The AKCA has also published a handy book with many design details: Practical
Koi Keeping, Volume 1. You might also consult a local koi or goldfish
club.)
You may be wondering why you even need a pond filter. As I have already
noted, most ornamental ponds are 100-percent recirculating systems. Except
for rainfall or water changes by the pondkeeper, no new water is added to
the pond. Under these circumstances, water quality declines fairly quickly,
and the pondkeeper must contend with consequent problems of fish health
and pond aesthetics. A properly designed filtration system can significantly
slow the decline of water quality, although no filter can maintain the pristine
conditions of an open aquatic system, such as a spring fed pond.
The accompanying table, entitled "Primary Effects Of Pond Pollutants,"
summarizes the fish health and aesthetic effects of the three basic types
of pond pollutants: nitrogenous wastes, suspended and settled solids and
dissolved organic carbon. The most serious water quality problem for the
pondkeeper, by far, is control of nitrogenous wastes - in particular, ammonia.
Unfortunately, you cannot have fish in your pond without also having ammonia
constantly being added to the water. Fish continuously excrete ammonia
through their gills, and additional ammonia is released into the pond water
by the decay of fish feces and uneaten food. Moreover, almost any organic
matter - solid or dissolved - likely to fall into your pond can be partially
mineralized into ammonia.
Ammonia appears to hinder oxygen uptake in the fish's blood. Lethal concentrations
can build up rapidly in heavily stocked ponds. Continuous lower concentrations
of ammonia cause chronic physical stress that ultimately reduces a fish's
ability to fight disease. Gill filaments become irritated and begin to
swell. This cuts off the oxygen supply to the membrane cells, which then
become infected with bacteria. Kidney damage has also been observed under
these conditions. Low concentration ammonia-related stress also reduces
food consumption and growth, inhibits reproduction and causes premature
death.
Bacterial action on ammonia produces toxic levels of another nitrogen
compound, nitrite. Nitrite, like ammonia, interferes with the ability of
the fish's blood to transport oxygen. Other bacteria convert nitrite to
nitrate, which is much less toxic to fish. (For complete information on
this process, see the article "Understanding The Nitrogen Cycle"
in this issue - Ed.) Contrary to popular belief, the nitrate levels commonly
found in ornamental ponds do not affect goldfish and koi in any measurable
way. Toxic effects do not show up until levels reach several hundred parts
per million.
Any materials that do not dissolve into the water are considered to be
solids, which can vary from microscopic particulates, such as tree pollen,
to large objects, such as leaf and tree fragments. Suspended solids are
undissolved materials that stay afloat in the water (though not necessarily
on the surface), circulating around the pond. In an ornamental pond, suspended
solids may be composed of fine mineral particles, which flow into the pond
via rain, wind, ground runoff and so on, detritus (a composite of finely
ground-up organic and inorganic material originating from plants and animals)
and plankton, the microscopic plants and animals that dwell in the pond.
The greater the quantity of suspended solids in the water, the higher
the turbidity. One of the most common causes of high turbidity in
ponds is planktonic algae, which turns the water pea soup green. From an
aesthetic standpoint, not only does turbidity reduce transparency through
the water, but it also makes the pond look dirty. In addition, some forms
of suspended solids can also irritate fish gills, causing stress and making
the fish more susceptible to disease. Fancy goldfish seem to be especially
sensitive to turbid waters, whereas koi and pool comets (a variety of goldfish)
appear to be totally unaffected.
Settled solids drift to the sides and bottom of the pond. Unless disturbed,
they tend to sit where they land. Koi keepers know, however, that these
fish constantly stir up settled matter, adding to the turbidity of the water.
Admittedly, the distinction between suspended and settled solids is somewhat
artificial, because under very quiet conditions and with enough time, many
suspended solids will settle out. Then again, many settled solids can be
resuspended by stirring up the water. In either case, even though these
solids ultimately leave suspension, they affect the aesthetic and biological
qualities of the pond.
Suspended and settled solids are composed largely of organic matter and
thus are susceptible to decay. Bacteria in the water will convert (mineralize)
some of this matter into ammonia, which then adds to the overall nitrogenous
waste burden in the pond.
Another water quality concern is dissolved organic carbon (DOC). DOC
consists of carbon-based compounds (excluding carbon dioxide and carbonates)
that are the metabolic by-products of pond life. Carbohydrates, proteins,
amino acids, fats, phenolic compounds and pheromones (hormones that affect
the behavior of other fish) are just a few examples. Concentrations of
DOC may be as low as 1 part per million (ppm) in clean rivers and lakes,
whereas polluted waterways may have levels up to 100ppm.
The bacterial decomposition (mineralization) of some forms of DOC will
add directly to the ammonia load in the pond. DOC can affect fish health
by supporting populations of disease-causing (pathogenic) bacteria and parasites.
It can also have a direct biological affect on fish when pheromones are
preset, inhibiting growth and lowering disease resistance. What is important
in this latter case is the origin and composition of the DOC, not necessarily
the total DOC concentration. On the one hand, in ponds with very light
fish loads, the primary source of DOC will be the metabolic products of
plants and planktonic algae. Cellulose-decomposing bacteria will dominate
the water's bacterial population, and only very low concentrations of fish
growth and immune system-inhibiting DOC will be in the water. On the other
hand, in heavily loaded ponds, the fish are the main source of DOC, and
the composition of the DOC is quite different from lightly loaded ponds.
This DOC will support rich populations of "protein-eating" bacteria
and fungi, some of which can cause disease in fish. The much greater concentration
of fish-originated DOC will directly suppress fish growth and immunity,
making the animals more susceptible to bacterial and parasitic infections.
DOC pollution is of greatest concern when the primary source of DOC is
the fish load.
The implications of all this are clear: Your pond must have some mechanism
for controlling the relative concentrations of solids, DOC and nitrogenous
wastes if your fish are going to live and thrive. Some ponds can handle
these pollutants without any supplementary filtration, whereas other ponds
require substantial assistance.
The question then becomes, do I need a pond filter. Whether or not your
pond will need a supplementary filtration system depends on the kind of
pond you plan to manage, and how you manage it. Let me draw a useful distinction
between a garden pond and a fish pond. A garden pond is a
attempt to recreate an ecologically balanced system among plants and fish.
The key here is that the amount and variety of plants are high, while the
quantity of fish is very low. I have seen many gorgeous examples of garden
ponds. They vary in size, but all have the same common features: the plants
are the primary attraction and the fish are almost secondary. For example,
Maryann Palmer's pond is a garden pond in which there is a total of about
150 grams (5.25 ounces) of fish on 1500 liters (400 gallons) of water.
This works out to a ratio of 0.1 kilogram (0.22 pounds) of fish per 1000
liters (1000 kilograms, 265 gallons) of water.
A typical garden pond might be kidney bean shaped - 8 feet long, 5 feet
wide and 2 feet deep - and hold about 550 gallons (about 2080 liters).
(Smaller and larger garden ponds are common.) Plantings would include several
waterlilies, a variety of submerged plants such as Anacharis, Cabomba
and Myriophyllum, floating plants such as water lettuce or water
hyacinth, and assorted bog plants such as iris and horsetail that rise out
of the water. Fish in the pond would be limited to perhaps a pair or two
of goldfish or several small koi.
This garden pond depends on ecological balance instead of filtration
to maintain water quality. The fish load is intentionally kept very low
so that the pollutants they produce can be handled by the bacteria, plants
and microscopic flora and fauna that populate the pond. Most of the solids
settle out of the water - resulting in low turbidity - and a considerable
amount is broken down by bacteria in the pond. Of course, an occasional
hand skimming of leaves and other debris helps maintain low solids levels.
Concentrations of the DOC we are most concerned about remain low because
1) the fish load is low, 2) mineralization removes some DOC and 3) partial
water changes remove some DOC. Lastly, the level of nitrogenous wastes
produced in the pond remains low (because the fish load is low) and is rendered
harmless by the activity of nitrifying bacteria living on the pond walls
and plants. The nitrate produced by nitrification is consumed by the plants.
No supplementary filtration is required.
In order to maintain this balance, no additional fish are added. As the
fish grow, the fish load is kept constant by judicious culling. If spawning
occurs, the new arrivals are quickly removed so as not to upset the balance.
In contrast, a fish pond is dedicated to the breeding and showing of
fish. Its primary purpose is to raise fish for display, as is the case
with most ornamental koi ponds. Here, the fish dominate the plants, and
often there are no plants at all. Fish loads are quite high - far in excess
of what you would ever find in nature. There may be 1 to 10 kilograms (2.2
to 22 pounds) or more of fish for every 1000 kilograms (1000 liters, 265
gallons) of water. This is roughly 10 to 100 times the load found in garden
ponds. Most fish ponds I have seen tend toward the high end! In John Ritchie's
case, for instance, the fish load is about 1.8 kilograms (4 pounds) of fish
per 1000 liters (1000 kilograms, 265 gallons) of water - 18 times the load
in Maryann Palmer's pond.
There is simply no way to achieve an ecological balance in such cases,
and therefore substantial supplementary filtration is needed. The solids,
DOC and nitrogenous wastes are produced in quantities far in excess of what
the population of bacteria in the pond can handle. Moreover, most of the
solids and DOC are of fish origin, increasing the importance of removing
them. They will just accumulate over time until the fish begin to get sick
and die - tragically bringing the pond back into balance.
Because pond conditions vary so widely - much more so than a conventional
home aquariums - pond filtration needs vary as well. Some ponds may only
have a problem with the accumulation of solids and turbidity; others may
only need a means of removing nitrogenous wastes. More than anything else,
the fish load will determine how you should assemble your pond filtration
system Below, we will discuss the component parts of supplementary filtration
for fish ponds, examining various alternatives for removing solids and DOC.
In part two, we will consider methods for controlling nitrogenous wastes.
Reducing solids requires some type of mechanical filtration that physically
removes solids from the pond water. There are two basic approaches worth
considering: gravitational settling and physical screening.
Gravitational settling is a process by which solids denser than water
eventually drift to the sides and bottom of the pond under the force of
gravity. You may have noticed that pond turbidity frequently increases
in the aftermath of a heavy rain storm as materials are washed into the
water and previously settled materials are stirred up. Subsequent settling
activity usually leads to substantial clearing in a few days. Essentially,
any pond is a settling basin. But rather than allowing this matter to settle
anywhere in the pond, is is better to either direct settling to occur in
a specific part of the pond or to have settling occur in a special basin
outside the pond to facilitate removal.
In the first instance, a special depression - a sump - is built into
the pond floor (Figure 1). Over time, settlable solids drift down into
this area, where a bottom drain, a siphon or a pump is used to remove this
material. Although a sump is simple, it has two problems: 1) a sump cannot
be added after the pond is built and 2) koi and goldfish love to muck around
in sumps, stirring up debris.
A preferable alternative is to add a settling basin outside the pond
(Figure 2). The settling basin is a transitory waterway through which pond
water is pumped. It is big enough so that solids settle out before the
water returns to the pond. The advantages of a settling basin are that
it can be added to a pond system at any time, it is not accessible to the
fish and draining and flushing are simple.
How big should the settling basin be? All else being equal, the time
required for a given particle to settle out depends on its density, shape
and size. Dense, small, round particles settle out faster than less dense,
larger, flat particles. In general, for our 100-percent recirculating pond,
the larger the settling basin volume is in relation to the pond volume,
the greater the amount of solids that will settle out.
Taken too far, this could get quite absurd, with the settling basin approaching
the size of the pond! So, let me suggest a more reasonable rule of thumb.
What little research has been published suggests that settling times of
15 minutes or more are required to remove heavier wastes. Thus, we want
the pond water to spend at least 15 minutes moving through the settling
basin before it goes on to the next part of the filter system and ultimately
returns to the pond. For reasons that will be explained in part two of
this article, we also want to pump one complete pond volume through the
filter system at least every two hours. These two criteria suggest that
the settling basin volume should be roughly 1/8th the total pond volume.
For instance, a 1000-gallon pond should have a settling basin that holds
about 125 gallons.
To improve operating effectiveness, the basin should be about 2 feet
deep and slope upwards towards the end where the water exits (see Figure
2a). A drain valve should be placed at the deep end for daily solids removal.
The effectiveness of settling basins can be improved further by the intermittent
placing of objects in the basin to restrict the flow of water (see Figure
2b). Brushes, fiber mats or any other form of partial barrier can be used
to slow the velocity of suspended solids in the water, forcing them to settle
out. In this way, smaller basins can serve larger ponds.
An advanced form of gravitational settling - one more appropriate for
intensive fish farming and rearing ponds with very high fish loads - involves
the use of "hydroclones" and centrifuges. These devices accelerate
pond water around a circular route at rates many times that of gravity (Figure
3). Thus, solids separation is more rapid and effective compared with ordinary
gravitational separation in sumps and basins. Because accelerated gravitational
separation is so much more effective, a hydroclone or centrifuge system
can be smaller than a standard settling basin, and may be worth considering
in situations where space constraints prevent construction of a simple settling
basin.
A hydroclone for a typical ornamental pond might be a cone 1 or 2 feet
in diameter, tapering down to 3 inches as it reaches a depth of several
feet. Water enters at the top of the hydroclone and is directed along the
cone's outer wall at high velocity. Solid wastes settle to the outer wall,
drift downward and drop out through the sludge outlet at the bottom. Clean
water exits from a pipe placed about 1 foot below the surface at the center
of the cone. Commercial units are available, although they are quite expensive.
The alternative to settling is screening. For our purposes, a screen
can be any porous barrier with a fixed mesh size that is placed in the flow
of water (see Figure 4a). Coarse screens - such as a grid of 1/2-inch PVC
pipe spaced 1/4-inch apart, or egg crate lighting grills - can be used to
remove leaves and other large debris. Window screening stretched across
a frame will trap particles down to a few millimeters in diameter. Thin
foam sheets and nylon floss held between two egg create lighting grills
can provide very fine mechanical filtration. Cleaning involves daily washing
of the screens, and intermittent replacement.
Even better mechanical filtration can be obtained with a somewhat different
"screen:" a gravity sand and gravel filter (Figure 4b). In this
design, water flows over a layered bed of sand and gravel and then trickles
down between the grains. The scrubbed water exits at the bottom of the
bed, leaving the solids behind. Gravity sand filters require daily backwashing
to keep the bed from clogging.
Although the quest for ever finer mechanical filtration might seem worthwhile,
keep in mind that the better the screen is at removing solids, the more
frequent will be the cleaning requirements. At the extreme, diatomaceous
earth filters certainly offer the best capability for removing ultrasmall
particles, but they are totally impractical for pond filtration. They are
so effective that they literally require hourly backflushing and cleaning.
The do-it-yourselfer has a wide variety of options for building a mechanical
screen filter. The size, mesh size and number of stages can be varied.
Personal experience suggests that you will get more mechanical filtration
and fewer maintenance headaches if you keep your filter screens thin but
give them a large surface area.
There are several commercial alternatives available as well. Danner Manufacturing
(160 Oval Dr., Central Islip, NY 11722) sells a thin foam screen wrapped
around a plastic cylinder under the product name Supreme Poolmaster Universal.
This filter is very effective for small ponds (under 500 gallons); several
can be ganged together for larger ponds.
Another option - one that is most suited for large ponds over several
thousand gallons - is the standard swimming pool pressurized sand filter.
Using a coarse sand (1 mm in diameter) or even #3 aquarium gravel, pressurized
sand filters are very efficient mechanical scrubbers. Although a pressurized
sand filter is easy to install and operate, there are a number of drawbacks
to these units. First, the pumps used with rapid sand filters consume lots
of electricity and are very noisy. Unless you have some remote place to
house the filter, the noise can ruin the pond setting. Second, daily backwashing
means high water consumption: a couple of hundred gallons per day. Third,
because the sand bed is quite deep, over time it tends to clog to the point
where backflushing is useless. Once this happens, the filter sand must
be replaced.
Keep in mind that the solids removed by a mechanical filter of any design
remain in contact with the pond water until they are flushed from the filter.
They are still "available" for bacterial decomposition that will
degrade water quality. Therefore, as I have already noted, you should flush
the mechanical filter as least once each day. Less frequent cleaning means
that the results of mechanical filtration will be largely cosmetic.
Of course, it is quite feasible to combine a settling basin with mechanical
screening; designs are open to the imagination. You could, for instance,
start with a settling basin with a water course of brushes, followed by
a coarse mesh screen, and end with a fine sand bed.
We now move to the topic of removing DOC. DOC removal in standard freshwater
aquariums is commonly accomplished with the use of granular activated carbon
(GAC). GAC, however, is quickly fouled by particulate matter, planktonic
algae and other substances that abound in the average ornamental pond, but
which are much more scarce in aquariums. A 1000-gallon (3785-liter) pond
might require 8.8 pounds (4 kilograms) of GAC or more each month! Thus,
GAC is not a practical approach to DOC control in ornamental ponds unless
you are quite wealthy.
Frequent partial water changes will, of course, keep DOC levels down.
But this can get very expensive with large ponds, and many parts of the
country are experiencing water shortages that limit such activity. Moreover,
if your fish pond is heavily stocked, nothing short of a 50-percent water
change every other day would matter.
An alternative method for removing DOC is the foam fractionator (more
commonly known as a protein skimmer). This is a simple device that uses
a rising column of bubbles to extract the DOC from the water. In fact,
you have probably seen foam fractionation at work in your pond without realizing
it. The appearance of a white scummy froth at the base of a waterfall is
caused by bubbles coated with DOC.
Foam fractionation works by adsorption, taking advantage of the fact
that many DOC molecules have a polar structure, with one end that is attracted
to water and one end that is repelled by it. The repelled end will attach
itself to the surface of air bubbles rising through a column of water, and
when the bubble is removed from the water the DOC molecule goes with it.
Foam fractionators for hobbyist pond use are not available commercially,
but they are quite simple to build using ordinary PVC pipe (see sidebar
entitled "Building A Pond Foam Fractionator" and Figure 5). Water
is pumped into the foam fractionator through a standard spa jet. A valve
placed before the spa jet controls the water flow, and here again the flow
should allow at least one pond volume turnover every two hours. A constriction
in the throat of the jet - called a venturi - causes a pressure drop as
water moves through the nozzle. An air tube is centered above the venturi
and air is drawn into the water flow at the pressure drop. The air-water
mixture moves up the fractionator column and adsorption occurs. The DOC-enriched
foam collects at the top of the column and ultimately builds up to the point
where it spills out through the exit port. The water moves back down the
column in a counter-current flow and is stripped of additional DOC before
swinging down and around to the water exit column.
You can operate the foam fractionator on its own pump, independent of
the main pond pump, or you can hook it in series or in parallel to the main
pond pump. The most important thing is to move approximately one pone volume
through the foam fractionator every two hours. This means that large ponds
could require several units ganged together.
Depending on the conditions in your pond, it may take a few hours or
a few days before your foam fractionator begins to produce results. Do
not be surprised if the foam you get is not as thick and rich as the kind
that bubbles out of marine aquarium foam fractionators. Freshwater systems
tend to produce "thinner" foams. You can adjust the foam by playing
with the three regulating mechanisms until the consistency is as thick as
will flow smoothly.
In the second half of this article, I will discuss the design criteria
for the last component of our supplementary pond filtration system: the
biological filter for detoxifying nitrogenous wastes. The final task will
be to combine the three elements together.
Steve Meyer raises koi and goldfish. He also designs and builds custom
garden ponds in the New England area.
Building a Pond Foam Fractionator
The main body of the pond foam fractionator consists of two columns attached
at the bottom by a 180-degree elbow. The larger column is the main column
(A) where DOC adsorption occurs. The smaller column - the water exit column
(K) - stabilizes the water level in the main column and allows clean water
to exit. It is important to note that the water outlet (L) must be lower
than the top of the main column, where the foam will exit.
The main column (A) is constructed of 4-inch PVC pipe. It should be roughly
8 inches long. The top is fitted with a 4-inch-to-2-inch reducer (B).
A small section of 2-inch PVC pipe © - which will vary in length depending
up your particular situation - connects to a 2-inch-to-1-inch reducer (D).
Lastly, a section of 1-inch flexhose (E), which serves as the foam exit
port, is attached to the top and lead away from the pond.
The bottom end of the main column is fitted with a 4-inch by 2-inch sanitary
T-fitting (F). The 2-inch opening will house the water inlet spa jet (G).
The air tube (H) for the spa jet must extend above the water level in the
main column.
Below the sanitary T-fitting is a 2-inch-long section of 4-inch pipe,
followed by a 4-inch-to-3-inch reducer (I). Next comes the 180-degree turn,
composed of two 90-degree elbows (J). The water exit column is made of
3-inch PVC pipe (K). IT is about 10 inches long and is fitted with a 90-degree
elbow (L) on top.
This foam fractionator uses three regulating mechanisms. First, as already
mentioned, the water exit column (K) controls the height of the water in
the main column. Second, a valve (M) is placed before the water inlet to
regulate the venturi effect in the spa jet (G). Third, the actual length
of the small section of 2-inch PVC pipe © on the top of the main column
can be adjusted to alter the consistency of the foam.
If you place the foam fractionator in the pond or settling basin, there
is no need to cement this unit together. You certainly do not want to cement
the top section, which may require adjustment over time.
All the parts you will need to build a pond foam fractionator are available
at your local plumbing supply store, except the spa jet. Spa jets can be
purchased at any pool and spa retail outlet. The last item you will need
is a pump (or you can tap off your main filter pump).
