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Related FAQs: Algae and Their Control in Aquarium GardensAlgae Control In Aquarium Gardens 2,

Related Articles: Algae Control in Freshwater Aquariums by Bob Fenner, Dealing With Algae in Freshwater Aquaria by Neale Monks, (some) Algae (in moderation) Can Be Your Friend, ppt presentation, Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, by Bob Fenner, SAEs in the Aquarium Garden, Otocinclus for the Aquarium GardenLoricariids/more than Plecos, and Snails

/The Aquarium Gardener Series

Algae and Their Control in the Planted Aquarium

Bob Fenner

Green filamentous algae

What a quandary! The same sorts of chemical and physical conditions, nutrients, temperature, lighting... that promote plant health and growth also sponsor algal profusion. What's an earnest aquarium gardener to do? A number of possibilities come to mind; principally to harbor an appropriate amount of plant material, with just adequate light and feeding parameters.

But what if algae "take over" anyway? Should you panic? Must you turn to chemical warfare to eradicate these simpler photosynthetic organisms? Hopefully not. By understanding what the algae are, design, setting-up and maintaining your system properly outright blooms can be avoided, and "hair", "scum" and "slime" algal types may be kept to a minimum.

The Players: Algae

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. The collective name of all but the blue-green algae, the sub-kingdom Thallophyta, meaning "all about the same plant body", refers to this simplicity of structure. Thallophytes may appear as attached or planktonic threads, sheets, smears, or single cells, coloring the water in sufficient concentration.

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; all aquariums will have some algae growth...

Algae Groups Include:

1) Blue Green Algae- 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, sheets, threads and chains.

I have yet to see a case where blue-greens arose or became entrenched in a "healthy" system. Be wary of polluted, high nitrate and/or phosphate conditions should these noisome bacteria-plants show up. Algae eaters will shun them and if water changes and other interventive means don't work, you may be compelled to effect a complete tear-down.

Two microscopic pix (about 100X magnification) of Blue Green "Algae" (Cyanobacteria). Oscillatoria and Aphanizomenon species.

2) Green Algae- are the most commonly encountered forms; they're found everywhere; occurring as floating, attached as "beards", "brushes", and spots, even swimming shapes and seasonal surface blooms.

Zygnema, a green filamentous algae, here involved in a form of reproduction between strands termed conjugation. The grass green circles are the plasmids called chloroplasts. BGA lack nuclei and such observable organelles. 

3) Brown and Red Algae- These are mostly marine; you probably know the larger ones as kelps, attached seashore forms. There are some filamentous "beard" red algae in freshwater as well as some "sheet-like" and seemingly encrusting forms. These are usually Blue-Green/Cyanobacteria that are mis-identified, but able to be discerned easily under a microscope on the basis of their simple morphology.

4) Diatoms and Dinoflagellates- are single celled, microscopic algae, ubiquitous, and mostly beneficial in terms of nutrient cycling, oxygen production, and competition with undesirable forms. Though diatoms may appear as brownish scums, they rarely cause problems in planted aquariums.

Diatoms, along with dinoflagellates, these microscopic single-celled algae produce most of the oxygen on this planet. Here is an electron micrograph of Biddulphia showing the porous nature of the silicious diatom skeleton, and it's use as diatomaceous earth in coating and trapping particles in filters. And a shot of green live diatoms. These algae often are the cause of light brown "scums" or smears on aquarium walls or substrates; rarely as causes of "green water".

A live dinoflagellate. The two "whips", or flagella you can make out encircling the median groove and along the individual cell's body.

5) Other Algae Groups: Euglenoids, golden brown, yellow green algae and others that are generally not a problem in captive aquatic systems.

Overview of the Algae & Aquariums

Under the happiest of circumstances, you won't even notice their presence if slight; they can even be beneficial functionally and esthetically, but in profusion algae are unwelcome guests. Don't despair; algae are easily controlled if understood. Most can be avoided by designing and building your system to reduce light, and nutrient availability; algal proliferation, related problems can be lessened through regular maintenance.

In terms of success, 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:


1) Chemical Activity: Algae thrive more in harder, alkaline water. It is advantageous therefore to limit the contribution of minerals via tap water and decor items to the system. Rocks and other decorations should be checked for reactivity. A simple assay involves breaking off a small piece of material, boiling it in water, allowing to cool and testing the cooled water with a simple pH or alkalinity test kit for increased value.

2) Circulation: Most algae do better under stagnant conditions. Keep your water in motion with filtration or water-moving pumps.

3) Light and Heat: The more intense the light over the longer period of time, the more the algae will grow. Aquatic plants, circulation waves, shade from floating or emersed vegetation all help to reduce light penetration, but barring other influences too much light will drive algal proliferation. Please see more complete articles for full descriptions of light quality and quantity.

4) Filtration: We need to define some terms for a more complete discussion of different forms of filtration. Particulate filters aid water quality by removing sediment that provides space and nutrients for algae growth. Chemical filtration: the use of water-softening clays and carbons may go some distance in preventing full-on blooms if incorporated in your filter scheme.

Biological filtration is the key factor in keeping your system balanced in your favor. This is the intentional and incidental use of live microorganisms and plants, preventing algae growth by conversion and removal of nutrients from the water.

5) Plants: Are most useful in controlling algae. They cut down on light and use the chemical food otherwise available to algae. Fast growing types such as Vallisneria, water sprite, Salvinia duckweed, and oxygenating grasses are among many excellent choices.

6) Pollutants: Control of these is very important. Food for algae mainly comes from feeding your livestock, fertilizing your plants. Be careful using intentional fertilizers (soil supplements, daily, weekly, at-water-change "drops") in your system. Do not use organic manures or terrestrial plant fertilizers in aquariums; a very small amount can produce several orders of magnitude weight in unwanted algae growth. If anything, you want your water to test nutrient poor; no measurable free phosphate and less than 10ppm total nitrates.

Frequent, partial water changes are the order of the day for all kinds of aquarium gardens. They are the best way of diluting nutrients.

7) Preventing introduction of algae or their spore beginnings. There are reasonable (e.g. dips such as aluminum sulfate), to harsh (bleaches) washing of new to-be-introduced plants along with quarantine of fishes (to flush their G.I. tracts)... Most of these efforts are futile in so much that algae will find ways to get into your system; and the damage to your livestock is not worth it. Instead, strive to keep your aquarium garden balanced in your favor, and learn to not sweat the small amounts of algae that will make it known to you that maintenance is due.

Control Methods:

So much for prevention; let's discuss ongoing problems. The same desirability in order of approach applies here: biological, then mechanical, lastly chemical.

Biological Controls: Algae Eaters

Snails are probably the most widely used scavengers, but are not generally 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. If you intend to utilize custodial mollusks, employ large, captive bred and raised species.

But don't give up on invertebrates entirely; there are some small semi-transparent shrimps that have proven to be competent algae eaters. Glass or grass shrimp in the genus Palaeomonetes variously sold as "feeders", and the oriental marsh shrimp Cardina japonica are great if your fish will leave them alone.

On the other hand consider algae-eating fishes; but be wary. Of the several species used some are far more appropriate than others. In the sucker-mouth south american catfish family Loricariidae, the species that stay small of the genera Otocinclus, Ancistrus, Rineloricaria, Loricaria, Peckoltia are the most desirable. Beware of the larger "plecos", mostly Panaque, Farlowella, Hypostomus, Pterygoplichthys and Plecostomus on the market as these quickly grow to become cruising bully-boys that knock over and damage plants.

Smaller individuals of the minnow-like fishes (Family Cyprinidae, subfamily Cyprininae), including barbs and the Siamese flying foxes (or the alternative acronym SAE for Siamese Algae Eaters), of the genera Epalzeorhynchus and Crossocheilus are excellent. Of less use is the hillstream fishes (genus Gyrinocheilus, family Gyrinocheilidae) commonly sold as "Chinese algae eaters" in the west; these have a habit of "going lazy" as cleaner-uppers with rapid growth, changing their eating habits to include their tankmates and your plants.

The livebearers called platies and mollies (family Poeciliidae) can also be useful as algae pickers, especially effective for hair algae.

The better algae control fishes may be stocked at about one per five gallons as small individuals, and their diets supplemented with boiled or frozen vegetable matter, pellets, flakes...

Mechanical Controls: Second best to prevention and biological controls are manual methods of algae control. Routine scrubbing or scraping of aquarium walls and vacuuming during partial water changes is principally what we're talking about here.

My personal favorite as an "algae scrubber" for both glass and acrylic aquariums is Eheim's (tm) "flocken" filter "wool". Excellent as a tool and non-scratching. Second best are regular spun "dacron" filter media. For really hard "spot" algae, a stiff credit card is hard to beat.

Chemical Means: Other than utilizing chemical filtrants, using chemicals to control algae is the least desirable route in terms of cost, safety and long term effect. All algicides harm live plants to some extent.

There are several brands of chemical algae killers on the market, most are either copper, simazine/princep or diuron/karmex based. Other than narrow ranges of efficacy the problem with algicides is that they treat symptoms only without dealing with the cause(s) of algae problems; i.e. what are the factors that are contributing to this system being out of balance? Remember this; all algicides are to some degree poisonous to other livestock; be careful.

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 comprehensive form of:

1) Proper system set-up, filtration and water circulation.

2) Minimizing nutrient availability by under-feeding, preventing excess fertilizer from getting into the water.

3) Using your test kits to measure nitrates and phosphates in particular and keep them at an acceptably low level through desirable plant growth and water changes.

4) Stocking and maintaining plant material as necessary to cut down light and nutrient availability.

5) Manually removing algae and nutrients through pruning, vacuuming, and water changes.

6) If absolutely necessary, tearing down and re-setting up the system or lastly, stooping to the use of chemical controls; most preferably copper compounds.


Given light, water and some chemical nutrient base, there will be algae life; if not started via the water source, food, plants, other livestock, then through aerial spore invasion. Some algal life should be anticipated in all aquarium gardens, and not looked upon as totally detrimental.

Algal problems are a symptom of a system being "out-of-balance"; principally too much nutrient base and light, with too little purposeful photosynthesis. In a properly set-up system algal anomalies are rare; inadequate upkeep is generally to blame for control problems. Excess nutrients from fertilization, feeding and soil should be solved by plant growth or diluted via regular water changes. Excess light situations are scarce, but can be easily remedied by removing wattage or cutting back on daily light period.

The easiest solution to algal outbreaks of "bloom" intensity is simply adding more fast-growing desirable plant life, limiting light and nutrient availability. Mechanical means, chemical filtrants, adding plants and biological helpers should be enlisted way ahead of any chemical algicide.

Lastly, some good should be mentioned of the benefits of having some algal growth. Algae do provide "fixed carbon" food and oxygen for fishes and invertebrate livestock while taking up some noxious cycled waste products. Indeed, some are truly attractive life forms, granting your system a more natural look.

Bibliography/Further Reading

Baensch, Hans A. & Rudiger Riehl. 1993. Aquarium Atlas, v. 2. BAENSCH, Germany. 1212 pp.

Beste, C.E. 1983. Herbicide Handbook of the Weed Science Society of America, 5th ed. Weed Sci. Soc. Am., Ill. 515 pp.

Brunner, Gerhard. 1973. Aquarium Plants. T.F.H. Publications, NJ. 159 pp.

Castro, Alfred D. 1996. Algae al fresco; exactly which algae eater really likes to chomp down on this stuff? AFM 12/96.

Fenner, Bob. 1991. Copper algicide use in pools. FAMA 6/91.

Frank, Neil. 1986-7. Algae in the aquarium. Parts 1-4. FAMA 10-12/86, 1/87.

Frank, Neil. 1996 Control of red algae in the freshwater aquaria, pts. 1 & 2. FAMA 11,12/96.

Frank, Neil & Liisa Sarakontu. 1995. Algae eating cyprinids from Thailand and neighboring areas. The Aquatic Gardener 8(2):3,4/95.

James, Barry. 1986. A Fishkeeper's Guide To Aquarium Plants. Salamander Books, U.K.. 117 pp.

Kutty, Vinny. 1992. It's about algae. AFM 5/92.

Kutty, Vinny. 1993. Algae eaters. The Aquatic Gardener 6(3):5,6/93.

Minor, K.I. 1995. What is that? Part 1: Diatom. FAMA 5 /95.

Nelson, Joseph S. 1994. Fishes of the World, 3d ed. Wiley, NY. Prescott, G.W. 1970. How to Know The Freshwater Algae. Wm. C. Brown Co., Iowa. 348pp.

Riehl, Rudiger & Hans A. Baensch. 1987. Aquarium Atlas, v. 1. MERGUS, Germany. 992 pp.

Riehl, Rudiger & Hans A. Baensch, 1996. Aquarium Atlas, v. 3. MERGUS, Germany. 1103 pp.

Roe, Colin D. 1967. A Manual of Aquarium Plants. Shirley Aquatics, England. 111 pp.

Stemmermann, Lani. 1981. A Guide to Pacific Wetland Plants. U.S. Army Corps of Engineers, Honolulu. 118 pp.

Stodola, Jiri. 1967. Encyclopedia of Water Plants. T.F.H. Publications, NJ. 368 pp.

Tommasini, Ron. 1992. Tricks and traps of the trade; # 1 Algae control. FAMA 9/92.



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