The Control of Algae in Ponds
by Robert Fenner
Reprinted with permission, from Bob's website in San Diego: www.wetwebmedia.com
Aquarticles
After battling algae infestations for twenty years in the waterscape maintenance
business, I learned to look carefully at systems that never had algae problems. Yes, there
are such set-ups, and you can have one too.
Perhaps you'll be one of those fortunate people who make adequate provision in the
design and construction of your water effect to preclude having "green water"
problems. If not, or due to nutrient laden water and intense light you have "green
soup" or you'd like an introduction to the whys and wherefores of algae and their
control, read on.
The simplest oxygen-producing organisms on this planet are the algae. They are for
the most part autotrophic (self-feeding), have no complex organizations and no sexual
reproduction. They contain chlorophyll and other pigments, but have no true roots, stems
or leaves.
Algae occur wherever there is sufficient light for photosynthesis, water and
nutrients; In fresh and salt water, in soil, hot springs, snow, even on and in plants and
animals. Along with some fungi, there are algae that live on bare rock as lichens in such
forbidding areas as the Arctic. This is their world.
Algae Groups Include:
Blue Green Algae/Cyanobacteria: More closely related to bacteria
than other algae they are often the scum on polluted, under-aerated/circulated,
over-fertilized waters. They are typically bluish-black and slimy. Forms include single
cells, clusters, threads and chains.
Green Algae: Are the most commonly encountered; they're found
everywhere. Occur as floating, attached, swimming forms and seasonal surface blooms.
Brown and Red Algae: These are mostly marine; you probably
know them as kelps, attached seashore forms.
Diatoms and Dinoflagellates: Are single celled, microscopic algae,
ubiquitous, and mostly beneficial in terms of nutrient cycling, oxygen production,
competition with undesirable forms. Though diatoms may appear as brownish scums, they
rarely cause problems in ornamental water features.
Other Algae Groups: Euglenoids, golden brown, yellow green algae
and others that are generally not a problem in captive systems.
Overview of the Algae
Sometimes they're beneficial functionally and esthetically, and other
times unwelcome guests, the algae are easily controlled if understood. Most can be avoided
by designing and constructing your system to reduce light, and nutrient availability;
algal proliferation, related problems can be lessened through regular maintenance.
In terms of long term cost, safety and ease of use, algae control methods can be
divided into three categories on the basis of most to least appropriate; these are
biological, mechanical and chemical controls. A few pertinent facts hold for all methods:
Prevention:
Chemical Activity:
Algae thrive in harder, alkaline water. It is advantageous to render the non-water
part of their environment chemically inert. Rock and concrete should be treated to lessen
reactivity with the water. When constructing, this may involve acid-washing to leach out
alkalinity, use of plastic cements, foundation coatings.
For non-biological systems it is most appropriate to coat the basin/s with a
sealing material. Some proper types are asphalt emulsions, chlorinated rubber paints and
epoxies. Marine paints and others may be formulated to be toxic; read the labels
carefully.
Rocks and other decorations should be checked for reactivity. They should not be
detectable by smell or taste; or they may be checked by chemical analysis. This applies to
all rock, including the waterfall, that comes in direct contact with the water. A simple
assay involves breaking off a small piece of material, boiling it in water, allowing to
cool and testing the cooled water in a container with inexpensive "test fish".
Circulation:
Most algae do better under stagnant conditions. Keep your water in motion
with air pumps and/or pumps.
Light and Heat:
The more intense the light over the longer period of time, with the deepest
penetration to the bottom, the more the algae will grow. Aquatic plants, circulation
waves, shade from trees, walls, lathe, screen will help. Make your system's sides as steep
and deep as possible and safe. Color the basin/s as dark as possible to reduce light
reflection. Black is the best despite it's heat absorptive properties. During
construction, dyes can be added to the concrete. The lower and more stable the temperature
the better.
Filtration:
Please see the Pond Filters pieces for a more complete discussion of different
forms of filtration. Particulate filters are least useful, but do aid by simply removing
sediment that might provide space for algae growth. Chemical filtration is generally
unrealistically expensive, but use of water-softening clays and carbons may go some
distance in preventing full-on blooms if within your budget.
Biological filters
Of several designs for systems with livestock, if properly engineered, are the key
factor in keeping your system balanced in your favor. You can win by launching biological
warfare with bacteria cultures purchased at a tropical fish store and having these
micro-organisms live in your filter, preventing algae growth by removing nutrient from the
water.
Plants:
Are useful in controlling algae. They cut down on light and use some of the
nutrients otherwise available to algae. Water hyacinths, water lettuce, duckweed,
alligator grass, lilies, oxygenating grasses are among many excellent choices.
Pollutants:
Control of these is very important. Food for algae comes from feeding your
livestock, fertilizing your plants. Be careful using fertilizers around your pond, a very
small amount can produce several orders of magnitude weight in unwanted algae growth. Keep
soil, toys, children, basically any and everything else out of the water.
Frequent, partial water changes are the order of the day for all kinds of aquatic
gardens. They are the best way of diluting nutrients.
Control Methods:
So much for prevention; let's discuss ongoing problems:
Biological Controls:
Algae Eaters: Snails are the most widely used scavengers, but not always a good
choice. Snails carry diseases for fishes as well as humans. Many are bisexual and hard to
control population-wise, others die mysteriously, polluting the water.
Re-read about snails and check with your local aquatic garden regarding appropriate
available species. Some fishes, like small koi, Dojos (Misgurnus anqullicaudatus) are
useful as biological controls.
Mechanical Controls:
Second best to prevention and biological controls are manual methods of algae
control. Routine brushing of the basin walls and vacuuming helps during partial water
changes.
Two of my favorite all time tools for pond-keeping are a razor-blade equipped
hoolah-hoe I saw first at the Disneyland Hotel in Anaheim's koi pond for giving string
algae a "crew-cut", and PVC pipe notched at the end to catch, twist, turn and
remove hair algae. Hmmm, I'm developing a strong desire for spaghetti!
Complete clean-outs acid and/or bleach washes are sometimes appropriate. Rock salt
is a good abrasive to use in scrubbing biological ponds leaving some algae behind.
Another type of mechanical/physical control involves the use of ultraviolet
sterilizers (which we'll cover separately) to chop up the DNA of free-floating algae, and
protein skimming (aka foam fractionation) with or without ozone to remove algae
"food". These high-tech. options are only mentioned here in passing as being too
pricey and touchy for the majority of ponderers.
Chemical Means:
Using chemicals to control algae is the least desirable route in terms of cost,
safety and long term effect. With most chemical algaecides you can't have live plants.
There are several brands of chemical algae killers on the market, many of dubious
value. The problem being they treat the symptoms only without dealing with the cause(s) of
the algae problem, i.e. what are the factors that are contributing to this system being
out of balance? Beyond this, all algaecides are to some degree poisonous to other
livestock; be careful.
If you do use algaecides, keep a close eye on the dosage and be on the lookout for
below acute toxic side effects.. Several products state that under "bad
conditions" the dosage may be doubled or tripled. If your water starts foaming and
your fish start gasping heavily at the surface, remove the fish or change a large part of
the water.
An Integrated Management Approach:
Realistically, you will have to do what everyone else does; call on
all the above mechanisms to balance the degree of cleanliness/lack of algae with the costs
of maintenance. Controlling algae should take the form of:
1) Proper construction, filtration and water circulation.
2) Minimizing nutrient availability by under-feeding, preventing run-off and excess
fertilizer from getting into the water.
3) Using your test kit to measure nitrates and keep them at an acceptably low level
through desirable plant growth and water changes.
4) Using shading as necessary to cut down light and heating.
5) Manually removing algae and nutrients through vacuuming, netting and filter
backwashing.
6) If absolutely necessary, stooping to the use of chemical controls; most preferably
copper compounds.
A Conclusion:
After all this talk of controlling algae, it ought to be pointed out that sometimes
it's better to "let it be". Algae growth is an indication of a normal, healthy
state. Within moderation, algae help keep the pond balanced and stable. The trick lies in
the word moderate. If you can keep the algae groomed, in one desired area or cropped to a
short length on the walls of your system, this will be to your advantage. By having
desirable forms, you can reduce the incidence of algae blooms.
Algae come in many shapes, colors and sizes. Many are beautiful, and often fish do
well in algae-infested waters. If you want to control algae in your pond at least enough
so you can see your fish, the above suggestions will help.
Bibliography/Further Reading
Blasiola, George C. 1991. Controlling algae in garden ponds; a review of
preventive measures. Pet Age 3/91.
Ford, David. 1986. Why does my pond go green? FAMA 6/86.
Hanby, David S. Swamp filter... a revolution in pond keeping. FAMA 2/96.
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