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/The Conscientious marine Aquarist

Algae and Their Control in Marine Systems

By Bob Fenner

 A Ctenochaetus Tang

New Print and eBook on Amazon
Marine Aquarium Algae Control

by Robert (Bob) Fenner

Talking about the algae with most aquarists reminds me of the sixties definition of "weeds", "Plants that we have yet to find a useful purpose for". Algae do have their place. They've been here for at least a billion years; and due to their ability to occupy almost all niches are going to be here way past our time.

Given water, light, some nutrient base, algae are going to invade and proliferate in your system. The focus here will be on preventing and controlling undesirable forms. Similar to our discussion of filtration, the principal categories of algae control can be categorized as prevention, biological, mechanical, physical and lastly chemical.

There are two categories of people; those who classify things into groups and those who don't. Okay, I'm trying to be funny; but there are two groups of algae: those that you want and those that you don't. Various types of algae serve different functions. At the simplest, they're bio-indicators, giving you a good sign that your system is biologically sound (at least they're growing in it). Some algae are incorporated in specialty filters ("scrubbers"), and all are useful for "removing" nutrients through bio-accumulation. Much algal matter, small and large is used as food. And let us not forget the great stretching exercise we've all gotten trying to clean them from tank walls, gravel, ornaments...

Then there are the purposely grown macro-algae. macro versus micro-, meaning you they're big, you can see them with the naked eye. At this time, these are mainly the green algae, especially the genus Caulerpa. Currently the Greens (Chlorophyta) are the only popularly exploited group, a real shame, and one that will no doubt change soon. I've included a short piece on the brown algae, and the book has two other "algal" Sections, 4 D) ii) Algae that are diseases, and 7) D) Preserving algae as art. I dream of future re-writes where we'll cover the gorgeous Red algae and more.

For right here and now, let's review what the major algae groups are, some of their interesting biology, and then a detailing of how to avoid undesirable "micro-algae", followed in the next Section by how to grow the macro-algae.

General Biology:

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. As a scientific assemblage the Blue Green algae are generally grouped with the bacteria; the rest of the algal "super-groups" along with the fungi are placed in a Sub-Kingdom called Thallophyta, meaning "all about the same plant bodies" in reference to the lack of specialization of their cells. For the most part, and for all our purposes, the botanical classification schemes dividing algae into Divisions (the equivalent of animal taxonomy's Phyla) is based on simple, observable color (The Green algae, Chlorophyta are green, the Reds, Phaeophyta are red...). Unless Chapter's Publishing insists, we'll dispense with scientific algae names and just use capital letters to denote a group at the Division level.

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.

The algae (and BGA) include:

1) Blue Green Algae aka Cyanobacteria 

Because they're  more closely related to bacteria than other algae they are often the scum on polluted, under-aerated/circulated, over-fertilized waters. They are typically slimy to the touch. Forms include single cells, clusters, threads and chains. The presence of this group is a danger sign in marine aquaria; usually something is seriously amiss filtration/circulation wise.

2) Green Algae 

Most commonly encountered; found everywhere. Occur as floating, attached, swimming forms and seasonal surface blooms.

Bryopsis, a pest Green Algae genus (!) a Snail (hopefully eating it) and a Pipefish head. 

3) Brown and Red Algae 

They're mostly marine, most common as the kelps, attached seashore forms. There are many smaller, even encrusting forms that "reef" aquarists come in contact with, sometimes to their chagrin.

4) Diatoms and Dinoflagellates

These are single celled, microscopic algae, ubiquitous, mostly beneficial in terms of nutrient cycling, oxygen production, competition with undesirable forms. Though diatoms may appear as brownish scums on tank walls, decor and gravel, they rarely cause problems in marine aquaria. One exception is the genus of Dinoflagellates called Amyloodinium (formerly Oodinium) a real infectious disease scourge.

Although at least five of the algal Divisions are known to have symbiotic species that reside within invertebrates, the dominant forms are Dinoflagellates. These algae live in mutually beneficial relationships, taking up wastes and carbon dioxide, and providing their host with fixed carbon (e.g. sugar) and oxygen. The predominant reef-building corals bear these symbiotic zooxanthellae. See Delbeek (1987) Tullock (1988) and Hoff (1985).

5) Other Algae Groups: There are a few but we'll just mention:

Euglenoids, Golden Brown, Yellow Green Algae and others that are generally not a problem in captive systems. Sometimes beneficial functionally and esthetically, other times unwelcome guests, algae are easily controlled if understood. Most can be avoided by designing and constructing your system to reduce light, nutrient availability, other problems can be lessened through maintenance.

Control Methods:

Can be divided into three or four categories: In general on the basis of most to least appropriate in terms of long term cost, safety and ease of use these are biological, mechanical, physical and chemical controls. A few pertinent facts hold for all methods of algae control. What's worth, "A pound of cure"?


1) Chemical Activity:

Algae thrive in nutrient rich water. It is advantageous therefore to initially provide as little "food/fertilizer" for them on setting-up your system. I take exception with most authors on the virtues of one salt mix over any particular other, and the special treatment (reverse osmosis, deionization, distillation) of the freshwater to make it up. These do little to restrict the introduction of nitrates, phosphates, other chemicals of use to algae. Instead, aquarists would do well to pay attention to more important sources, such as gravel, other decor, feeding, and the addition of "trace elements", vitamin, and other adjunct "mixes". The last three contribute far more to algae proliferation than any tap water and synthetic mix.

2) Circulation: 

Most micro-algae do better under stagnant conditions. Keep your water in motion with air pumps and/or fluid-moving pumps.

3) Light and Heat: 

This is a tricky area. If you are a fish-only or fish and non-photosynthetic invertebrate keeper, your situation is much simpler. For the most part, the kind, amount, and light-dark cycling of your system will be a matter of personal taste; what looks good to you. Alternatively, reef-keepers, other folks wanting to grow algae, people with invertebrates hosting endosymbiont algae are going to have to strike a balance of favoring desired algae over those they want to avoid. Of the proper wavelengths, this comes down to not too much, or too little duration and intensity. As a practical corollary; often, for your particular circumstances, more intense light over longer photoperiods favor macro-algae over micro. In other situations, the opposite holds true. More specifics on these parameters are offered in the next Section.

Similarly, and tied together with high-heat-output lighting, there is an ideal range for the forms of algae you want and those you don't. Here comes another broad generalization. Most of the algae offered in the trade hails from the Caribbean, particularly Florida. It grows best in waters in the seventies (degrees F.). Many of the runaway algae problems I've seen were due to the water being too warm (in the mid-eighties) and fluctuating too much, negatively impacting the health of the desired algae and other livestock.

4) Filtration: 

Please see the set-up and sub-pages for a thorough re-discussion of different forms of filtration. Particulate filters are least useful in algal control, but do aid by simply removing sediment that might provide space for algae growth. Chemical filtration is generally unrealistic, but use of carbons may go some distance in preventing full-on blooms. Most of the products sold around the world as nitrate, phosphate "removers" are worthless; either they don't work at all under the conditions, or minimally allowing too high dissolved concentrations.

Biological filters of several designs, if properly engineered and operated, are the key factor in keeping your system balanced in your favor. You can win by launching biological warfare with bacteria cultures, having these microorganisms live in your filter, preventing algae growth by removing nutrient from the water.

Foam fractionators, aka protein skimmers reign supreme in preventing micro-algae; they are tops in expediently removing organics that might otherwise fuel pest-algal growth.

5) Macro-Algae: 

Are useful in controlling micro-algae. They cut down on light and use some of the nutrients otherwise available to undesirable forms. The fast growing Caulerpa and encrusting corallines (a group of Red algae resembling corals) are best. There is evidence that the latter produce chemicals that preclude the growth of micro-algae, especially the Blue-greens.

6) Pollutants: 

Control of these is very important. Food for algae comes from feeding your livestock, adding "trace", vitamin and other chemical "additives". Be careful concerning adding anything to your system. Wear dedicated rubber gloves to prevent pollution form your hands, arms. Algae are almost entirely composed of water; just a speck of solids from the above sources can produce several orders of magnitude weight in unwanted algae growth.

Frequent, partial water changes are the Order Of the Day for all marine systems. They are the best way of diluting nutrients. (see Section 5) C) vi). Advertisers who proclaim their products "do away" with water changing should be investigated as to the comparative costs of purchasing and operating their systems relative to overall advantages of partial changes.

Control Methods:

So much for prevention; you can see that except for limiting nutrients, all marine systems have all the requirements (water, light, heat, gas) to grow algae; let's discuss ongoing problems: 

Biological Controls: 

Turbo and Astrea snails, some blennies, some tangs, among others are good grazers. Snails are the most widely used scavengers, and generally the best choice. Some parts of the country seem to favor the use of sea urchins, dwarf angels... The former die too easily and move the decor about, and the latter can be problematical with eating expensive invertebrates.

Mechanical Controls: 

Second best to prevention and biological controls are manual methods. Routine brushing of the sides and vac-ing helps during partial water changes. Some acid and/or bleach washing of decor is sometimes appropriate.

Physical Controls:

 State of the art methods include functional protein skimmers, with or without ozone and ultraviolet sterilizers. These physical filters remove and destroy algae on exposure and help oxidize nutrients as the water is circulated.

Chemical Means:

 Using any chemical to control algae is the least desirable route in terms of safety and long term effect. There are several brands of antibiotic (Erythromycin, or equivalent generic name) on the market; all should be avoided. The problem being they treat the symptoms only without dealing with the cause(s) of the algae problem. What are the factors that are contributing to this system being out of balance? There are the obvious downsides of altering the chemical "evolution" of your system as well. Leave us not forget anti-biotic means "against life".

In commercial and Public aquaria settings copper, usually in some format of copper sulfate solution is employed as an algicide, as well as a general epizootic parasite preventative. If you have or ever intend to keep invertebrates, macro-algae, live rock in the system do not get involved in using copper. This metal is superb in treatment and quarantine tanks, dips and fish-only arrangements. The trade uses it extensively; but always keep in mind it is persistent and toxic to all life, especially non-fish.

If you do use a chemical algicide, 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 and change a large part of the water immediately.

A Conclusion:

After all this talk of controlling algae, it ought to be pointed out that sometimes it's better to "let it be". Micro- and macro-algae growth is an indication of a normal, healthy state. Within moderation, algae help keep the system 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 purposely having desirable forms, you can reduce the incidence of unattractive algae blooms. Should you experience a bloom, I'd review the above root causes and correct for them.

There are many varieties of algae that could, will be utilized by marine aquarists in the future. Some are "coming to light" with the operation of cold/cool water, surge, and other new specialty systems.

What about "true", flowering plants? Yes, some embryophytes are found in shallow marine environments; eel, turtle, and surf "grasses", even mangrove trees get some mention in the pet-fish literature. These are too obscure, sub-specialties for much more mention here; the curious Reader is referred to the Bibliography.

Bibliography/Further Reading

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

Black, Tom & Alex Bielawski. 1971. Algae culture. Marine Aquarist 2(2):71.

Blackburn, Wayne. 1989. Plants in the marine system.

Delbeek, J. Charles. 1987. The role of symbiotic algae in marine invertebrates. FAMA 11/87.

Dewey, Don. 1979. Marine algae, a key ingredient to the successful saltwater system, part 1,2, introduction and cultivation of marine algae in the aquarium. FAMA 8,9/79.

Emmens, C.W. 1991. Algae. FAMA 8/91.

Fenner, Robert. 1990. Ornamental marine algae; how to raise and market it., Macroalgae for marine aquaria. The Pet Dealer 2,10/90.

Fenner, Bob. 1991. Waterscape Maintenance: Copper Algicide Use in Pools. Freshwater and Marine Aquarium. 6/91.

Frank, Neil. 1986. Algae in the aquarium; part II: strategies for control. FAMA 11/86.

Gamble, Sam. 1995. Algae curse: a new view. FAMA 8/95.

Glodek, Garrett. 1993. A lesson in plant taxonomy and systematics. FAMA 11/93.

Graff, Rick. 1993. Getting control of micro algae; how to deal with this problem in reef tanks. AFM 1/93.

Hoff, Frank. 1985. Zooxanthellae. FAMA 11/85.

Marchant, Don A. 1992. Red hair and hair algae madness. FAMA 2/92.

Michael, Scott. 1995. All that algae; if it makes you feel any better, this is a common problem.

Olenik, J.E. with Mike Hoffer. The advantages of marine flora; the living flora that establishes itself in aquaria helps keep marine life healthy and makes the aquarium attractive. Here's a guide to the plants. Pets Supplies Marketing 4/91.

Paletta, Michael. 1990. Eliminating problem algae. Seascope, Aquarium Systems. Vol. 7, Fall 90.

Prasek, Edward D. 1995. Micro and slime algae: are they driving you crazy too? TFH 7/95.

Tullock, John. 1988. Zooxanthellae: symbiotic algae in invertebrates. Marine Fish Monthly 3(8)/88.

Wecsler, Lawrence H. 1975. Algae in the marine aquarium. TFH 2/75.


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