Reef Aquarium Basics

Corals are an important part of the beautiful reefs and can be found in tropical oceans worldwide. These animals have unique shapes and coloration that make them sought after by many aquarists. However, coral reef tanks are more demanding than most Fish-Only tanks. After years of research, experiments, new product developments, and a better understanding of their biology, corals are becoming easier to keep.

With proper maintenance and care, you can create a thriving reef in your home. Once you understand the needs of your corals and get the hang of how to balance your water parameters to their needs, keeping them becomes easier to manage.

Corals are one of the trickiest groups to compile a standard care guide as their needs are so widely varied. Provided here is a general guide of the care, requirements and parameters needed for a healthy reef aquarium. With research and dedication, keeping corals can easily be the most rewarding experience you have as an aquarist.

Which Corals Should I Keep?

Soft Corals

Soft Corals are generally easier to care for compared to most hard corals. Many soft corals do not require as strong lighting or the water flow most hard corals require and can tolerate a wider range of conditions. This group includes leather corals, polyps, mushrooms and corallimorphs.

Hard Corals

Hard Corals are often divided into Large-polyed Stony Corals (LPS) and Small-polyped Stony Corals (SPS). They have more demanding requirements for trace elements and minerals like Calcium, Magnesium and others and are more dependent on water quality and lighting than many soft corals.


Lighting is a critical consideration for the reef aquarium. If the lighting is too strong, you may bleach your corals. If the lighting is too low, your corals may need extra supplemental feedings or may not survive. LED fixtures are becoming more popular as technology advances. Metal halide lights are great for any coral that needs moderate or high lighting, but may be too strong for corals that require lower lighting. T5 & Compact Fluorescent lights are good for low to moderate light requiring corals, and multiple bulb units can be used in tanks less than 24" deep for higher lighting needs. Some corals have the best appearance under actinic lighting - lighting that emphasizes the blue and purple colors of the light spectrum. Lastly, some corals may prefer direct light while others prefer indirect. Lighting is an aspect of care that should be carefully researched for the specific corals you intend to keep.


Placing your coral in the proper area of your tank plays a big role in its overall health. Some corals should be placed low, while others may need to be placed mid-level or high in the aquarium. There are also corals that prefer to be placed on rock or other hard surfaces, while some should be placed on the substrate or on a sandy bottom. Corals that need less lighting can be placed on ledges or under overhangs and some actually do better in such conditions. Placement is dependent on your lighting and water flow. When placing your coral, you should also keep in mind that some corals have sweeper tentacles, some grow quickly, and some can expand. Therefore, these corals need to have adequate space between them and their neighbors and should be securely attached to make certain they do not fall.


Most corals have zooxanthellae (algae living in their tissue) that convert light to energy, which provides corals with much of the sustenance they need to survive. However, many corals need some supplementation in order to thrive. Knowing what to feed your corals, how frequently, and which method of feeding is best can be tricky.

Many LPS corals should be target fed foods like brine shrimp, mysis shrimp, or other small meaty foods that are small enough for them to take in and digest. Most SPS corals rely on lighting and their zooxanthellae and do not need to be target fed, though they are able to consume tiny particles.

Like many other invertebrates, there are also many corals that maintain their nutrition through filter-feeding. These corals should be fed suspended foods like marine snow, phytoplankton, or zooplankton. Some may prefer one type over the other, so make sure to research which type of food is best for your coral. When feeding a coral any of these filter-foods, it is suggested that you put the food near the powerhead so that the food can be pushed through the water column, making it easier for your coral to filter it out. It is also recommended to feed coral in two steps. First, feed a small amount to entice the coral to extend its polyps. After the polyps are extended feed the full dose. It may take a few minutes, but it helps make sure that food is not going to waste and your coral gets enough food. In regards to how frequently you should feed your corals, generally 2-3 times a week is sufficient. However, some may need to be fed more or less frequently, so research for specifics is highly suggested.


It is important to maintain proper levels of trace elements and minerals like Calcium, Magnesium, Strontium, Iodine, and Alkalinity for your corals to thrive. Some may be more sensitive to changes in these elements than others. All of these elements are important for hard skeleton-building corals, and may need to be dosed or supplemented. Soft Corals are less dependent on these elements, and supplemental dosing may not be necessary although some, especially Iodine, are necessary for shedding and disease/parasite control. Water changes are often enough to maintain the proper levels, but levels should be monitored by testing. Magnesium should be stabilized around 1,300 ppm. If it is not stabilized, there will be unwanted precipitation of calcium and carbonate ions. Once this is stable, you can work on your calcium and alkalinity. Calcium is one of the most talked about ions in reef tanks. It is critical for the formation of a variety of structures, including the skeletons and shells of many corals and other organisms. It should be maintained around 400-450ppm. Alkalinity is a measure of the ability of a solution to resist a decrease in pH when acids are added. Since the acids are normally produced by the biological action of the reef tank contents, alkalinity in closed system has a natural tendency to decrease. The proper level for alkalinity should be between 8-12 dKH and additives can be used to maintain this level.


Some corals can be aggressive, using several different strategies. Some may eat other invertebrates or fish by trapping it when contact is made (similar to the Venus Fly Trap plants on land). Some have sweeper tentacles that can sting other corals, invertebrates, fish, or even the aquarist. Others, particularly Leather Corals, can release toxins in a form of "chemical warfare" which may damage neighboring corals. Corals may be considered aggressive simply because they grow rapidly and may grow over or into other corals. Corals should be selected and placed appropriately to avoid conflict in the aquarium.

If at any time you have any questions or need help selecting fish or supplies for your aquarium, feel free to contact the fish room at 717-299-5691 ext. 1213 or You can also find informative articles on That Fish Blog at or post your questions on our Facebook page. We at That Fish Place - That Pet Place want to keep you and your fish happy for years to come!

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