Coral Info
Hard Corals
Hard corals have hard, calcium-based skeletons. Most hard corals -- also called stony corals -- consist of numerous single polyps living together in colonies. A single polyp consists of a sea-anemonelike organism that secretes the calcium-based structure of the colony's skeleton. If you look very closely at the polyp, all hard corals' polyps have rings of six smooth tentacles. Hard corals provide the majority of structure on coral reefs, with their dead skeletons becoming the anchors for other corals, including both hard and soft coral.
Soft Corals
Soft corals' chief difference from hard corals is structural. While hard corals secrete calcium-based skeletons, soft corals do not. Instead, soft corals contain structures within their tissues called spiracles that support their bodies. Additionally, soft corals have eight fuzzy tentacles for feeding. Aquarium hobbyists often consider zoanthids to be soft corals. While a biologist would consider zoanthids a type of sea anemone, for aquarium purposes, their care is identical to true soft corals.
Coral Care
Caring for Hard Corals
In terms of aquarium care, hard corals are among the hardest organisms to keep happy and thriving. In order to thrive in aquariums, hard corals need powerful lighting and supplemental minerals. Hard corals need about 5 watts of light per gallon of aquarium water. Since hard corals absorb calcium and other minerals to make their skeletons, you need to provide extra calcium. You can provide this with liquid supplements, calcium-rich substrates and specialized equipment like calcium reactors. You should always position hard corals at least 6 inches from each other, since many species unfurl sweeper tentacles to sting nearby encroaching corals.
Caring for Soft Corals
Soft corals require specialized care, but less than hard corals do. Still, both types of corals include a huge range of species, so exceptions exist in the form of difficult soft corals and easy hard corals. Soft corals still need calcium supplementation but less than hard corals, since soft corals need only enough to produce and maintain their spiracles. Most species of soft corals also need 5 watts of light per gallon. Keep in mind that many species of soft coral, particularly star polyps, button polyps and mushroom corals may reproduce rapidly, and spread across hard surfaces in the aquarium.
Lighting
Metal halide lighting
In tanks utilizing metal halide lighting, I suggest using the same system as described above, with a few addendums. First, for those corals that contain a lot of zooxanthellae (the symbiotic algae that lives in the coral's tissues), as indicated by their coloration being dark green or dark brown, in addition to starting these corals low it may also be necessary to initially place some type of screening material (eggcrate, fiberglass mesh, etc.) above them. This is necessary to prevent these corals from suffering from oxygen shock due to the overproduction of oxygen from the zooxanthellae when initially placed under bright light (Delbeek and Sprung, 1994). This screening material needs to be above the corals for two to three weeks to gradually allow the corals to acclimate. Once this is removed, the corals can continue to be acclimated as described above. This screening technique is also useful for tanks that are shallow (16 inches deep or less) where it is difficult to move a coral farther away from the light. In addition, during this time, the light cycle should be dramatically shortened to further reduce the risk of shocking the corals. Cutting the light cycle in half for the first week, and then gradually adding an hour to it each week is a good way to reduce the risk of light shock.In terms of placing the corals once they have acclimated, the general rule is the brighter the color of the coral, the closer to the lights it should reside. Thus, bright pink Bird's Nest (Seriatopora hystrix) or Cactus (Pocillopora verrucosa) corals usually should be placed higher in the tank than their brown counterparts. The reason for this is that the brighter color indicates pigments in the tissue have been produced to protect the coral from ultraviolet (UV) light that is present in the shallower depths (Delbeek and Sprung, 1994). Once a coral has been acclimated to this bright light and begins to grow, the growth tips will usually be of a brighter color than the original colony itself.This same pattern also holds for soft corals. Brightly colored soft coral colonies like Yellow Tonga Leather corals (Sarcophyton elegance), bright green Finger Leather corals (Sinularia sp.) and white Xenia colonies all seem to do better with brighter lighting than their brown or beige counterparts. If the lighting is inadequate for these brightly colored corals, these bright colors will gradually fade over time. Therefore, a good indicator of whether a coral is in the proper place and under adequate lighting is how its color compares with what it looked like when it originally arrived. If the lighting is better and the coral is acclimated properly, it is even possible to bring out the colors of a coral, so that over time, it may be more green or pink than when it was originally collected. This is the result of more UV light being present in our reef tanks than the coral was exposed to in the wild. Thus, to compensate for this, brighter pigmentation occurs.Under metal halide lighting, many corals can remain at the bottom of the tank. Mushroom anemones (Actinodiscus sp.), Plate corals (Fungia sp.), Tongue corals (Herpolitha sp.), and Brain corals (Favia, Favites, Symphyllia, etc.) all do quite well in the lower depths of these tanks. In addition, Elegance (Catalyphyllia) and Bubble (Plerogyra) corals seem to do better under metal halide lighting when placed lower and to the far sides of my tank. In fact, in my tank, the Bubble coral resides under an overhanging Leather coral and is doing quite well.
Fluorescent lighting
Fluorescent lighting is still the method of choice for most reef enthusiasts, particularly those keeping predominantly soft and large polyped stony corals. Fortunately, even in fluorescent lighting there are now many choices. In addition to standard bulbs, high output (HO) and very high output (VHO) bulbs are also now available, as well as compact HO and the very latest T-5 (HO) lights. As their names imply, these bulbs differ by the amount of light that they produce. It is my opinion, that for the majority of tanks housing soft corals and LPS corals, fluorescent lighting will provide all the light necessary to meet the animals' needs and allow them to thrive and grow. The goal should be to get between 4-6 watts of light per gallon of water over the tank.However, even with fluorescent lighting and more so with HO and VHO fluorescent lighting, care needs to be exercised when placing the animals under a new lighting regimen. This is because many of the lighting sources that we utilize contain more ultraviolet (UV) light than the corals are accustomed to on a reef. Because of this difference, I have found it advantageous to slowly acclimate new corals to artificial light. If the corals are not acclimated slowly, it may cause them to bleach or burn. This is particularly the case with the HO or VHO "blue" bulbs that we use, as well as with many of the metal halide lamps.For this reason, when I obtain a new coral, I usually place it at the bottom third of the tank for at least one month. After this one-month acclimation period, I gradually move it up to its desired final location over another two-month period. This may seem extreme, however, I view my tanks and the tanks that I have helped set up as long term, five-year plus projects, so there is really no need to hurry. I use this method for SPS corals, which show the least tolerance for being shocked, owing to the thin veneer of living tissue that is actually present on the colony. It is also useful for large polyped stony corals like Brain corals (Symphyllia, Favia), Open Brain corals (Trachyphyllia), Elegance (Catalyphyllia), as well as any other corals that contain a large amount of bright green pigment in their tissues. It has been my unfortunate experience, that if I immediately place these corals high up in the tank, they bleach and die very quickly. Because of this, I now employ this system of acclimation, and as a result, I have achieved much better results when adding new corals to a tank.