Reef Tank / Coral Aquarium

Coral reefs are incredibly diverse ecosystems, often described as “rainforests of the sea”.  Reefs occur in clear, shallow waters throughout tropical regions across the globe and a reef tank or coral aquarium is the epitome of an aquatic ecosystem for many home aquarists. Formed by the calcium carbonate skeletons, the backbone of the reef is built by tiny coral animals that make up large coral colonies. Coralline algae also produces calcium carbonate, which cements the all the other coral skeletons together, forming the continuous reef structure. Skeletons of tube worms, mollusks, and other organisms also become incorporated into the reef.

Coral reefs are important habitat and nursery grounds for fishes and invertebrates. They are often associated with mangrove and seagrass communities, providing protection from wave and storm damage. Disturbances to reefs may result in upsetting the ecological balance of the reef as well as having indirect impacts on other nearby habitats.

The reef-building corals can be identified by their stony skeletons made of calcium carbonate. A coral colony consists of thousands of individual coral animals, each similar in appearance to a small sea anemone with its base attached to a calcareous cup. Corals are usually armed with a ring of tentacles used to capture zooplankton from the surrounding water. Most reef-building corals also contain symbiotic algae, called zooxanthellae, within their tissues. These single-cell algae have a mutualistic association with the coral hosts, a relationship that benefits both partners. The algae utilize carbon dioxide and nitrogen-based waste products released from the coral. In return, the algae perform photosynthesis, producing sugars and amino acids. These products are transported to the coral in support of its nutritional needs.  Coral polyps are often withdrawn during the day, opening up at night to feed on zooplankton. During the day, the symbiotic algae located in the coral tissues, carry out photosynthesis.

Corals in the Aquarium

There are a wide variety of corals commonly sold in the aquarium trade.  Many of them are fast growing, hardy, and can be propagated almost as well as freshwater plants!  Others, specifically the Small Polyp Stony (SPS) corals have very demanding requirements and are difficult to grow, but once the requirements are met they can be propagated and are often aquacultured (propagated and not wild harvested) with is a huge plus!  Some are easy to care for but difficult to propagate and others still are neither easy to care for nor can be propagated.  Due to the stress the worlds coral reefs are in we recommend purchasing only corals that can be propagated that have preferable been aquacultured.  In doing so, you will be able to share propagations with friends or members of a local aquarium club or trade them with a local fish store for modest credits!  The important thing is you will be giving back to the valuable and amazing coral reefs and it’s inhabitants!

Mushroom Corals

Mushroom Coral

There are a wide variety of shapes and colors of mushroom corals available.  The great thing about mushroom corals is they are incredibly easy to care for and tolerate even marginal water conditions fairly well.  Their lighting requirements is really no more than for freshwater plants … about 1.5-2 watts per gallon fluorescent or 0.75-1 watts per gallon LED.  In fact, they will somewhat shy away from the bright lights often used in an SPS coral aquarium.  They will also naturally grow and propagate fairly quickly in an aquarium on their own.  This makes them great for not only beginners but also for tanks with fish such as dwarf angels that might nip at corals.  This also makes them well suited for tanks with fish such as Anthias or Squirrelfish that really prefer more subdued lighting levels.

Soft Corals / Leather Corals

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A “Toadstool” Leather Coral

Similar to the mushroom corals, the soft/leather corals are easy to care for, propagate, and do not generally need as strong of lighting as other corals.  They will need more than mushroom corals though and at least 2-3 watts per gallon fluorescent or 1-1.5 watt per gallon LED is required.  Be aware though, that some species such as the Carnation or Christmas tree corals do NOT contain symbiotic algae and really should NOT be attempted in an aquarium.  The corals commonly identified as leather corals, toadstool corals, as well as Star Polyps and Xenia “waving hand” polyps though are all fairly hardy, easy to care for, and will readily propagate in most systems.

Some soft and leather corals will put out chemicals that might negatively interact with other corals such as SPS corals in the tank.  We generally wouldn’t recommend mixing SPS and the soft or leather corals.  We’ve had coral systems where one species or another mysteriously will die for no apparent reason but do well in almost identical systems at other times.  Keep in mind that corals do engage in chemical warfare with one another or extend tentacles at night that can sting and damage other corals and this is a probable explanation.  It’s best to keep give corals their space for this reason.

These corals will also benefit from an active microfauna population or additional weekly feedings of micro-plankton or foods designed for filter feeders.

Polyp Corals

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A Xenia Polyp Coral

Some polyp corals such as Star Polyps and the Xenia “waving hand” polyps are usually grouped in with the Soft corals as they are not as colonial or individual as the other “Polyp” corals.  With these polyps, you will start getting into stronger lighting requirements as polyps may not share their food with the other polyps in the group as much so about 3-4 watts per gallon fluorescent or 1.5-2 watts LED is recommended.

These polyp corals are not quite as fast growing or hardy as the Star and Xenia polyps but are still fairly easy to grow and will propagate.  They also come in a wide variety of colors.

These corals will also benefit from an active microfauna population or additional weekly feedings of micro-plankton or foods designed for filter feeders.

Large Polyp Stony Corals

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A Green Bubble Coral, a Large Polyp Stony (LPS) Coral

The difference between the Stony Corals and the others discussed so far is that the Stony Corals will form calcium deposits and that is what help builds up the coral reefs along with corraline algae.  Large Polyp Stony Corals (LPS) are generally larger calcareous corals with large fleshy polyps.  Most of the LPS hard corals produce long sweeper tentacles which they use to keep any other organisms a safe distance away.  The degree of extension of the tentacles depends upon the amount of light, current, and whether the coral is feeding or not.

The LPS corals will usually require fairly strong lighting, about the same as polyps or even a bit higher, about 3-4 watts per gallon fluorescent or 1.5-2 watts per gallon LED.  They also will tend to have higher standards when it comes to water quality.  You will need to monitor calcium levels and make sure that stays in the correct range and you will want nitrates and phosphates as low as possible.  This means the use of denitrification and phosphate remover will likely be necessary with even a moderate fish load.

The LPS corals are slower growing than the other corals discussed so far and only some of them will be able to be propagated.  We personally recommend the species that can be propagated over the ones that can not.  It will generally take a few years before an LPS coral will double in size but when that happens to one that can be propagated, you just grew a brand new coral that won’t have to be harvested from nature!  Some species are even available online that have been aquacultured.

If you want to look for an LPS that can be propagated look for the “Branching” LPS corals.  The Hammer and Frogspawn corals can come on branching and non-branching varieties.  The Trumpet corals are also branching and can be propagated.

Most of the other LPS corals can not be propagated easily or not at all.  Some actually are hardy and easy to keep such as the Bubble and Cup corals.  The Brain corals are somewhat more delicate.  The Elegant coral although beautiful,  is pretty difficult to keep and not really recommended.  It is recommended you stay away from the non-photosynthetic “Tube” corals.  To keep them alive you will have to meticulously feed them at night!

Overall, we can say that the few branching LPS corals make a great and environmentally sustainable additions to a reef tank.  Otherwise, think twice and with many, you might be making a mistake unnecessarily damaging our world’s reefs.  We’d only recommend many of them if you are extremely dedicated and have the time and resources to keeping them alive and healthy as long as possible.

Small Polyp Stony Corals

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An Acropora Small Polyp Stony (SPS) Coral

Small Polyp Stony Corals (SPS) are usually branching and can be easily propagated so that’s a big plus.  The caveat is they require the best water quality and most intense lighting of all the corals and you will want at least a solid 4 watts per gallon fluorescent/Metal Halide or 2-3 watts per gallon LED.  As Metal Halides and Fluorescents are going out of style at least 2-3 watts per gallon LED will be recommended.  In addition, you will want them under the lighting directly and not that deep.

SPS corals include the Acropora species, Horn Coral, Montipora, Pavona, and Birds Nest corals.  If you keep SPS corals you will want to keep a light fish Bioload and avoid fish like anthias and squirrelfish that prefer subdued lighting as well as any fish that might nip at the corals as SPS will not tolerate that well.

You will need to monitor calcium levels and make sure that stays in the correct range and you will want nitrates and phosphates as low as possible.  This means the use of denitrification and phosphate remover will likely be necessary with even a moderate fish load.

Blue Ridge Coral / Fire Coral

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Blue Ridge Coral

Both of these species are in a slightly different categories genetically than the LPS and SPS corals but look and can be treated like the SPS corals.  If anything, they are hardier and easier to keep than the SPS corals.  They are also easy to propagate and are actually incredibly common in the world’s oceans.  They are more rare in the aquarium trade but are a GREAT find if you can pick one up!  Personally, we think they are an overlooked part of the aquarium hobby.

Milleporina, commonly referred to as fire corals, are hydrozoans. They are common throughout the Caribbean and Atlantic reefs. Fire coral is named for the nematocyst-containing defensive and food capturing polyps. Nematocysts contain a coiled barb, trigger, and neurotoxin. Upon stimulation, the trigger shoots the barb, which releases the neurotoxin upon entering the prey or predator.  It will make the back of your hand a little red and itchy buy that’s about it.

The Blue Ridge Coral, sometimes referred to as the Blue Coral, is often mistaken for a small polyp stony (SPS) coral because it has a hard blue exoskeleton with long, thin polyps. It really is an octocoral (soft coral) and its growth forms are branching, plate-like, columnar, or encrusting. Its body is composed of calcium carbonate and iron salts, which lend its distinctive blue color. However, the polyps are either brown or light blue. They are an interesting and peaceful coral that will add diversity to your reef aquarium.  The Blue Ridge Coral is generally peaceful towards other corals in the reef aquarium and will do best added to a well-established tank.

They both requires moderate to high lighting with a medium to strong water current in the aquarium. Calcium, strontium, iodine, and other trace elements will need to be added to the water.  They also both contain the symbiotic algae zooxanthellae from which they receives the majority of its nutritional requirements through photosynthesis.   However, a little phytoplankton feeding and some microfauna in the aquarium system are appreciated by them as well as most corals.

Gorgonians / Sea Fans

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A Gorgonian or Sea Fan

Anthozoans include soft corals, gorgonians, stony corals, and anemones. The subclass Octocorallia consists of the soft corals including gorgonians. On Florida’s reefs, soft corals are common in various forms ranging from encrusting mats to large sea fans. Gorgonians, including sea fans, sea plumes, and sea rods, are well-adapted to wave action with flexible skeletal materials and strong holdfasts that attach to the bottom substrate. Zoantharia includes the order Scleractinia, the stony corals. These corals are distinguished by a stony, calcareous skeleton. Each coral polyp is enclosed in a calcium carbonate cup-like structure. These cups are cemented together, forming a coral colony of thousands or millions of polyps.

These polyps are withdrawn during the day, opening up at night to feed on zooplankton. During the day, the symbiotic algae located in the coral tissues, carry out photosynthesis. The algae release some of the compounds produced via photosynthesis to the host, while receiving nutrients from the coral in the form of waste products including ammonia and phosphates. Both symbiont and host benefit in this mutualistic association.