The key to maintaining healthy corals over the long term, be they delicate Acroporids or more hardy sessile invertebrates such as zoanthids, is stability. The more stable you as an aquarist can maintain the chemical composition and other environmental factors in your captive reef the less any inhabitant in the aquarium will have to expend energy to adapt to change. The closer those parameters are to those encountered in the coral’s natural habitat, the ‘happier’ they will be and the more likely they are to survive.
Corals need to grow in shallow water where sunlight can reach them. Corals depend on the zooxanthellae (algae) that grow inside of them for oxygen and other things, and since these algae needs sunlight to survive, corals also need sunlight to survive. Corals rarely develop in water deeper than 165 feet (50 meters).
Corals need clear water that lets sunlight through; they don’t thrive well when the water is opaque. Sediment and plankton can cloud water, which decreases the amount of sunlight that reaches the zooxanthellae.
Warm water temperature: Reef-building corals require warm water conditions to survive. Different corals living in different regions can withstand various temperature fluctuations. However, corals generally live in water temperatures of 68–90° F or 20–32° C.
Corals are sensitive to pollution and sediments. Sediment can create cloudy water and be deposited on corals, blocking out the sun and harming the polyps. Wastewater discharged into the ocean near the reef can contain too many nutrients that cause seaweeds to overgrow the reef.
Saltwater: Corals need saltwater to survive and require a certain balance in the ratio of salt to water. This is why corals don’t live in areas where rivers drain fresh water into the ocean (“estuaries”).
Soft corals are the ‘non-reef building’ corals of the reef. When they die, they melt away completely leaving no skeleton behind. This lack of skeleton gives the corals a much greater degree of flexibility and a softer feel than their skeleton growing counterparts, from which their common name of ‘Soft Corals’ is derived. These corals are also some of the most popular and most commonly available corals found in our hobby. This guide will focus on the photosynthetic softies, which are generally considered very easy to keep. They derive their food from predominantly the products of photosynthesis. Generally most soft corals are found in the wild beside many hard corals and while many of these hard corals are more difficult to keep the softies are easy to keep. The soft corals tend to be more tolerant of different water conditions and thus easier to keep. Non-photosynthetic soft corals such as brilliantly colored Carnation Corals or many of the non-photosynthetic Gorgonians are also commonly available, but are much more difficult to keep because of their constant feeding requirements.
Large Polyp Stony, or LPS, is a hobbyist term used to describe certain types of corals. These corals generally have very large, distinct fleshy polyp(s) over a hard-calcareous skeleton. Many kinds of corals are included in the group, from brains to chalices, hydnophora to caulastrea. These varieties will also lead to a certain amount of variability in care and optimal conditions. However, there are some basic general guidelines that may be applied to most members of the group and will aid in their care.
Many LPS corals have large obvious mouths, and will accept meaty foods like mysis shrimp. For some, this feeding is an optional supplement while other species are unable to sustain themselves long-term solely on the products of photosynthesis and will gradually waste away if not fed.
For especially fleshy LPS, be sure to allow the coral to close before removing from water to prevent damage to the tissue.
SPS (Small Polyp Stony) is a hobbyist term used to loosely identify a group of corals that are at least somewhat similar in appearance and care. These corals always have hard skeletons and very small polyps - usually not much bigger than a pin head though there is no set size requirement. To the new hobbyist SPS corals such as Acropora, Montiporas, and Bird's Nest can be somewhat intimidating. These stony corals come in an incredible variety of colors and growth forms that can be absolutely stunning. However, their care requirements are generally a step or two above the usual beginner corals like softies and LPS.
Moderate to intense lighting, good random flow, and clean, stable water quality are key with these corals. Properly maintained they can grow quite quickly. Growth forms include branching, plating, and encrusting varieties. Fortunately, their stony skeletons are usually quite easy to frag, making them favorites for propagation and trading.
Some SPS corals, such as those that are plating or have especially thin branches, can be somewhat fragile and easily broken. Care should be taken when working in your tank to prevent accidental fragging. Generally, SPS corals do not need to be fed directly and specifically feeding your tank for the sake of SPS corals is usually not recommended as this can lead to excessive nutrient levels and poor coloration. Strategic use of amino acids may be beneficial, but we recommend you do some research as this is a more advanced topic.