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Series: Livestocking Small: Pico, Nano, Mini-Reef's....... Marine Systems under 40 Gallons

Algae for Small Systems:  Some Standards


By Bob Fenner

Small Marine Aquariums
Book 1:
Invertebrates, Algae
New Print and eBook on Amazon:
by Robert (Bob) Fenner
Small Marine Aquariums
ook 2:

New Print and eBook on Amazon: by Robert (Bob) Fenner
Small Marine Aquariums
Book 3:

New Print and eBook on Amazon:
by Robert (Bob) Fenner


Algae, as in larger marine systems, are inevitable in viable smaller saltwater volumes. ALL bodies of water that can/will support larger biota have a mix of these simpler forms of photosynthetic life. As with bigger tanks, you want to be aware of the kinds and just how much algal growth is useful; and when you should react to noisome varieties like Blue Green “Algae” (actually more closely related to bacteria); and when to ignore to simply nudge your system in the direction you want it to go. In fact, the smaller the volumes you maintain, the more critical this observation and need for possible re/action becomes.

            To reiterate, don’t be surprised to find the usual “succession” of diatom, Dinoflagellate, even some BGA growing in your newly set up smaller marine systems. This event marks the continuation of establishment of cycling (a good thing); and will pass as your system matures. The situations in which there is too much algae; unaesthetic to overgrowing other life, and/or undesirable types should be addressed promptly.

            Here we’ll cover all basic ins and outs of what algae are, what allows them to proliferate, and their simple to more involved control by various means.

The “What” of Algae:
            Algae are (too) often referred to as “simple plants”; actually, they’re not true plants at all; lacking leaves, stems, flowers, xylem and phloem… other “real” plant structures. Most algal Divisions (a taxonomic category equivalent to zoology’s Phyla, singular Phylum) are grouped classed as “Thallophytes”, meaning “all about the same plant bodies”, in reference to their largely undifferentiated cellular make up. The hated Blue Green “Algae” are even “simpler” organisms, lacking nuclei, chloroplasts, having a single strand of circular DNA… They are classified in modern taxonomic schemes as photosynthetic bacteria, not algae.

            The diversity of Thallophytes, BGA is tremendous; they’ve been around as the first life on this planet onward; are microscopic single celled organisms to huge kelps of hundreds of feet length and tons in wet weight. Humans use them for medicines (e.g., agar in petri dish culture media), emulsifying agents for beer, cosmetics and more (alginates from brown kelps), foods (blanche mange, Nori…) and much more. For us as aquarists they can serve to modify: stabilize and optimize, our systems; act as food, beneficial competitors against less desirable forms, and even act as ornamental décor in their own right.

            So… for simplicity’s sake you can think of “algae” as a grouping of simple/r photosynthetic life; some of direct and indirect uses (in moderation) to us as aquarists; others being problematic (or indicative of problematic conditions) to possibly noxious via their competition or toxic metabolite production.

Algae: Good, Bad, Ambivalent

Blue Greens: & Red, Black…

Cyanophyceans are easily described on the basis of what they lack. At right is a photo-micrograph of Scytonema; note the lack of plasmids and nuclei… Blue greens come in all sorts of colors (see below), but are mostly scums or filaments; and all are all slimy to the touch. Transient populations of small size can be ignored, but persistent BGA presence and overabundance should be countered. BGA can be toxic to all other life and otherwise use up nutrients, biominerals you’d rather go to your purposeful livestock.


Some True Algae You’d Like & Not: There are many others

Greens, Division Chlorophyta:

There are several popular green algae… that can/will do most everything you’d like your algae to do: be edible, slow-growing, not overly encroaching, look nice… Some examples: Right: the past-popular genus Caulerpa; with many species (C. peltata here), continuous night/day growth, and unfortunate penchant for overgrowing and “going sexual”. Outlawed in many places.
Below, the old timey fave genus Halimeda and oh-so-delectable genus Ulva, Sea Lettuce. The current super-choice shown last: Chaetomorpha; the aptly named spaghetti algae


Some Green/Chlorophyte choices that are meh (!) to undesirable period! Folks used to over-react re Chlorodesmis (at right), but now spend good money buying colonies (!). Below, first row are images of innocuous Neomeris and one of the several “Bubble Algae” (Dictyosphaeria here); and two principal trouble makers, genera Derbesia and Bryopsis… best to be very pro-active with these last two, removing rock, scrubbing, possibly bleaching to limit their over-growth.


Some Browns, Division Phaeophyta

Most folks outright avoid Phaeophyte algae; which is a shame. Other than needing extra additions of iodide-ate, many are easy to grow and attractive. A couple of the more common “pro” species shown here. At right, a Dictyota species. At bottom left a Turbinaria in the Red Sea. And bottom right, an often vilified genus, Lobophora, for its propensity for spreading too much, too fast; though it occurs in some gorgeous red, green and grey varieties.


Reds, the fab Rhodophyta!


Red algae are always desirable… from the many encrusting varieties… rock hugging, plating and digitate (some examples below); to the fab genus Gracilaria (right) with hundreds of species. A premiere group for growing in refugiums; under low light conditions. Encrusting forms require high, consistent biomineral content (Ca, Mg) and alkalinity. Their only downside can be the difficulty of scraping them from your tanks viewing panels. Best to use a plastic tool, and keep up with this routine maintenance weekly.


Diatoms, Dinoflagellates… and more!


There are a few other less-notable algal groups (Divisions), but we’ll just mention two more that are made up of single celled species. Most aquarists consider them noisome; as tan-colored scums on their hard substrates; and worse. One of the Dino’s being the causative organism of Velvet Disease. These algae are easily avoided through simple maintenance procedures and having other photosynthetic life competition. At right, an overgrowth that’s likely mostly diatoms and/or Dinoflagellates. A micrograph of diatoms below, and one of a Dinoflagellate bottom right


Where From Art Thou Algae?

            Most aquarists don’t purchase algae specifically; instead having it “show up” as part of live rock, on other hard material with other livestock, or as spores or bits in a purchases bag of water. Rest assured, should you not intentionally add algae, they will still show up. Of course there are algae one can buy outright; some as pure cultures from business like Alga Gen.

            Best to plan on the fact that your system IS going to have algae; and better by far for this to be an intentional mix of species you desire; and to do what you can to favour this mix, in turn disfavoring those you don’t want.   


Approaches to Algal Control:

            Are several; here we’ll hit the highlights. There’s MUCH more depth covered on WetWebMedia.com as well as a recent ebook available on Amazon by me. The former can be viewed anytime for free, the latter can be borrowed by Kindle owners for free. Categorically control means are easily divided into prevention, restriction, competition and predation. All four should be considered and applied.

Prevention through restricting nutrient input:

            As the olde saw goes, “An ounce of prevention is worth a pound of cure”. You can most easily control nuisance algae by limiting chemical foods availability. First off this involves your source water. IF it has considerable nutrient base (e.g. Nitrates, Phosphates…) you should consider utilizing the most appropriate means of exclusion; for most folks this is reverse osmosis, but contactors, and more sophisticated gear is available for aquarists needing very few to a great deal of water volume.

            Be careful re adding foods, particularly any liquids… as these are most all “pollution in a bottle”; similarly frozen/defrosted foods should be net-rinsed in freshwater to remove solubilized non-nutritive food juice. Discreet foods (e.g. pellets) are best overall for most set-ups.

            Take care also in “mystery supplement” use. Many products on the market that don’t list their ingredients are worse than worthless. Avoid them.


            Restriction involves a mix of approaches to limit both the introduction of undesirable forms as well as diluting wastes that ultimately make their way as foods for chemo-auto-trophic and photosynthetic life.

            The process of isolating (quarantining) all new purchases for a few weeks accomplishes many good ends; one of which is allowing you to observe it for troubles, including unwanted hitchhikers. Placing acquisitions apart greatly diminishes the likelihood of introducing pest algae as spores and thalli.

            Restricting metabolite build-up is accomplished through your adherence to good maintenance practices. Frequent partial water changes in particular are key to diluting pest-algae fuel. Weekly change outs along with rotating chemical filtrant media, keeping your skimmer contact chamber and collection cup clean… all limit undesirable algae growth.


            Are organisms that compete with unwanted algae for nutrients, space and light/ing. This can be more than simply “fighting algae with algae”, as not only are there other photosynthetic life forms (e.g. corals and their relatives, some Nudibranchs and more), but often boosting/bolstering microbial auto-trophs, photosynthetic and not, as in dosing with carbon (e.g. vodka). Depending on your situation livestock and system make-up wise there are a few approaches to consider here.


            It stands to reason that all forms of life have their roles to play as prey. Determining what eats the particular kind/s of algae you want to get rid of can be a challenge however; with “reef safe” hermits for instance moving on to nibble most all else. Again, depending on the size, lay-out and types of pest algae you’re dealing with, you’ll need to investigate and experiment with herbivorous fishes and invertebrates of use.

Some examples of great algae eaters:

Atrosalarias fuscus (Ruppell 1838), the Brown Combtooth Blenny (though it can be yellow, very dark...). A popular reef aquarium fish for its prodigious filamentous algae feeding. Western Indian Ocean; Red Sea to Pakistan. To about four inches in length. At right: One in S. Sulawesi.


Mespilia globulus (Linnaeus 1758), the Blue Tuxedo Urchin (Sphere Urchin of science). Eastern Indian Ocean to western Pacific... in shallows amongst algae it grazes on. To three inches in diameter. Needs hard substrates, shady areas. Can be kept solitarily or in small groups. Eats mainly algae, including corallines. 




            The take home messages regarding small marine systems and algae are these:
Make your peace with them; because you will have some algae, therefore
Choose the types you want to have by favoring them over others you want to avoid
Limit ALL through care in avoiding introduction of excess nutrients, filtering and other means of dilution, and
Use competitors and predators that you know will delimit noisome algal proliferation


Bibliography/Further Reading:


 An e-book by the author on overall Marine Aquarium Algae, Control is available from Amazon, here: here

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