Jeremy outlines some of the best saltwater fish and invertebrates to tackle algae outbreaks in your reef tank.
The dreaded A-word: algae. Whatever area of the fishkeeping hobby you enjoy, I bet you've been frustrated at some point by this photosynthetic menace.
Freshwater keepers may opt for an army of Amano shrimps, some colourful nerite snails, or indeed a bristlenose pleco or two to control their green growths, but there are perhaps even more options available to the saltwater niche. Plus, many of these options are reef-safe too, helping to prevent algae from smothering your attractive, and perhaps expensive, corals.
Whether you are looking for a small invertebrate for a desktop tank, or an algae-grazing fish for your large reef, there will be a perfect option for you.
Related article: Back to saltwater: starting simple with beginner corals.
A Mix and Match Approach
The best way to combat nuisance algae is to combine many different types of algae-eating fish and invertebrates. This means algae is attacked on many fronts, and by many natural forms of algae-cutting and algae-consuming apparatus.
Algae grazers play a key part in coral reef ecology, and by keeping rocks free of algae, they allow corals to colonise, grow, and shade out nuisance algae in the future. It's the same aim in the home aquarium.
Large reef aquaria may combine every type of algae-eating fish and invertebrate listed below, all grazing algae on a daily basis and keeping the tank free of algae just as they do on a natural coral reef. Alternatively, a small nano reef may utilise just a handful of the small invertebrates.
Related article: Marine Hitchhikers: Natural pest Control For Reef Tanks.
Invertebrate Clean Up Crew
And it is with the invertebrate options we begin our journey into all things algae-eating. Let's dive straight in with a firm favourite.
All photos by Shutterstock unless otherwise specified
Sublime Snails
Snails are among the most widely available and commonly used algae-eating invertebrates, with several species suitable for the reef tank. Choose from black-footed Trochus, spiny Astrea, turban (Turbo spp.) and Tectus. Both Tectus and Astrea are often sold under the generic “turbo snail” moniker.
Turban snails are the most commonly offered, but also the least hardy. You’ll often find their empty shells on their sides, presumed dead after starving or not being able to right themselves. Once on their sides, they are also easy meals for hermit crabs, which both dine on their flesh and then live in their shells.
Black-footed Trochus snails (pictured below) are the best choice as they are hardy and can right themselves. They are long-lived in mature reef tanks and may even breed, too. They often arrive with algae on their shells, which is a good indicator of the type of environment they come from.
While snails can be effective algae eaters, they do need to be added in numbers – 10 or more in the average-sized reef tank. They also require instant access to nutritious green algae. If you place snails into a brand-new tank with no algae, they will starve, leaving an empty shell graveyard behind in their wake.
Snail Top Tip
When adding snails, ensure you place them the right way up in the tank so that their foot can take hold and they can protect themselves. Place them on a hard surface such as the tank glass or a rock, so that they can grip and clamp down if attacked.
If you drop snails in upside down, they may become an instant buffet for large wrasses and hermit crabs.
Humble Hermit Crabs
While we are on the subject of hermit crabs, along with snails, they are among the most commonly kept members of the clean-up crew (CUC for short). They also provide entertainment for new reefers who have never kept mobile invertebrates before. All hermit crabs live in the empty shells of molluscs, and require spare shells of the right type and size as they shed and grow.
There are over 800 species of hermit crabs worldwide, with many being either red or blue, so ensure you get reef-safe species which stay small, rather than the species that can grow large, eat corals, or bulldoze your reef as they go.
Species to look out for include:
- Rock hermits (Calcinus sp.)
- Red-legged hermits (Paguristes cadenati)
- Blue-legged hermits (Clibanarius tricolor)
- Halloween hermits (Ciliopagurus strigatus)
- Blue-knuckle hermits (Calcinus elegans)
All hermit crabs are actually omnivores and will graze on anything from algae to pellet foods and even dead fish. The challenge with hermits is keeping them sufficiently hungry to graze algae, but not so hungry that they target snails for their meat, as well as their shells.
Always provide at least one more shell than there are crabs, and be prepared to offer larger shells as they grow. Most reasonably sized reef tanks will require at least five hermits, but they should only be added once the algae has started to grow.
Mischievous Mithrax
Emerald crabs, often sold as mithrax crabs (Mithraculus sculptus), are among the few marine invertebrates specifically sought after for their appetite for bubble algae (Valonia spp.). Their flattened claws are well adapted for picking algae from between rocks, making them a useful addition to reef tanks where nuisance algae has gained a foothold.
Like hermit crabs, emerald crabs are opportunistic omnivores rather than dedicated herbivores. While many spend their days grazing algae, larger or hungry individuals may begin scavenging more meaty foods, and are occasionally blamed for nipping at soft corals or catching very small fish. While many remain model reef inhabitants, they are generally regarded as reef-safe with caution.
Emerald crabs are best kept singly, or in small numbers in larger aquariums, and should be offered supplementary foods once nuisance algae has been brought under control. Well-fed specimens are generally less likely to become troublesome.
Superb Sea Hares
Sea hares are a type of herbivorous sea slug, the species most commonly encountered being Dolabella auricularia. They can be quite large, up to 12.5cm (5”) long, and have voracious appetites, being able to clear a 120cm (48") tank of algae in just a few days, but there lies the catch.
Sea hares only eat certain types of filamentous algae; they consume them rapidly, and once they're gone, they face starvation. Many marine stores offer a buy-back scheme to their customers so that they can be passed around from tank to tank and not run out of food.
Sea Hare Top Tip
Sea hares are prone to being caught in wave pumps, so make sure you use a guard on all pumps!
Related article: Let's Talk About marine Shrimp.
Unbelievable Urchins
Sea urchins are popular algae grazers for reef tanks. They are coveted for their ornamental form and colours as well as their clean-up crew potential.
Several species are commonly available, including the large and menacing long spine urchins (Diadema antillarum), the small tuxedo (Mespilia globulus), pictured below, and the colourful orange spine collectors (Tripneustes gratilla). Sea urchins consume many forms of nuisance algae but will graze desirable coralline algae too, returning coralline-covered rocks to a white, bare state.
Related article: Urchin Clingfish: a reef oddity.
Urchins are also known to bite through wave pump power cables and even some soft corals, as well as bulldozing their way through coral frags, picking them up and sticking them to their backs as they do so.
Urchins should be considered for mature tanks with daily growth of algae, and some species may go for years without becoming a problem. Others become tiresome through picking up frags or grazing corals. If you want an urchin, make sure you secure your corals well!
Algae-Eating Marine Fish
With the algae-eating invertebrates covered, it is time to move on to the piscine janitors for your reef. Remember, many of these need larger aquariums than snails and hermit crabs, so you must always research each species in more detail to ensure they are suitable for your setup.
Related article: Beginner's Guide to Reef Tanks: Choosing The Right Marine Aquarium.
Terrific Tangs and Superb Surgeonfish
Tangs, or surgeonfish, are some of the best-known algae grazers and are a key part of healthy natural reefs as well as home reef aquaria.
Choose one of the Zebrasoma species which include: the yellow (Z. flavescens), purple (Z. xanthurum), gem (Z. gemmatum), brown (Z. scopas) pictured above, or sailfin (Z. veliferum). In large tanks with experienced owners, Acanthurus tangs can also work well, including: powder blue (A. leucosternon), pictured below, powder brown (A. japonicus), goldrim (A. nigricans), Achilles (A. achilles), orange shoulder (A. olivaceus), or freckleface (A. maculiceps).
Bristletooth tangs are popular algae grazers and not too aggressive, including tomini (Ctenochaetus tominiensis) and silver spot (Ctenochaetus truncatus), and large tanks could combine a tang from each of the above three genera.
Tangs are active, medium to large fish and as such need large aquaria in which to graze and exercise. If you cannot provide this, then they are not the algae control for you. They can also be territorial to their own kind, related species, or other algae-grazing fish which may resemble them or pose a possible threat to their food source. Careful stocking is often required.
If that’s not enough to cause you headaches, Acanthurus species are often also very whitespot-prone, even when quarantined.
Did you know?
Regal tangs (Paracanthurus hepatus), pictured below, don’t actually graze on algae as frequently as people assume, instead preferring to consume zooplankton that drifts over the reef.
Brilliant Blennies
Most blennies graze algae, and most stay small and are reef-safe. The algae blenny (Salarias fasciatus) is the most well-known algae-grazing blenny and is often purchased solely for that purpose, as its colouration is muted and camouflaged. Like the sea hare, algae blennies, often sold as lawnmower blennies, are accomplished algae grazers, and can be prone to starvation if sufficient nutritious algae growth is not present.
Photo by Alex Bell
The starry blenny (Salarias ramosus) is a similar alternative. Red spotted flymo blennies (Blenniella chrysospilos), are also good algae grazers, and bicolor blennies (Ecsenius bicolor) and tailspot blennies (Ecsenius stigmatura) graze algae too. Algae-eating blennies have cute Muppet-like faces and are great characters in any reef tank.
Related article: Characterful blennies for your reef tank.
Ravenous Rabbitfish
As the name suggests, rabbitfish are grazers, and are as good as surgeonfish for eating algae in reef aquaria. The foxface (Siganus vulpinus) is the most popular species and eats many types of algae, including bubble algae, although it requires a large tank when fully grown. Several closely related foxface species are also available and they all reach a good size.
Owners must be aware of the venomous dorsal spines when handling them.
Foxfaces aren’t to everyone’s taste and are mainly added for their algae-grazing abilities. They are prone to starvation in algae-free or underfed tanks, and hungry specimens are occasionally blamed for nipping corals.
Maintenance Still Matters
Even the best algae grazer is only part of the solution. Excess nutrients, poor husbandry, and inadequate water movement are the root causes of most nuisance algae outbreaks. Algae-eating fish and invertebrates should be viewed as part of a balanced maintenance routine, working alongside regular water changes, sensible feeding and good filtration, rather than as miracle cures.
Remember, you must be able to care for any algae-eating species you purchase for their entire lives. Check that you can sustain them once the algae is depleted, and that their maximum adult size is suitable for your marine aquarium's dimensions. These animals aren't just there to clean up some greenery and deserve the same amount of care, love, and respect as any other pet.