Corals

Corals have only become a widespread feature of saltwater aquariums in recent years, after a period of learning the best methods to keep them alive in tanks. Now it’s hard to imagine a home for saltwater fish without corals’ diverse array of complex shapes and vivid colors. Not only do they significantly heighten the visual appeal of a reef tank, but corals also impact water quality and provide shelter for fish. But they don’t do what they do for free. Like other organisms, they require food, light, and protection. And with so many different types of corals, caring for each could mean a meticulous and nuanced approach. Before diving into particulars, take some time to learn just what these things are and how they function.

Basics

Although they look a little like shrubbery at first glance, corals are actually colonial organisms, consisting of many tiny invertebrates called polyps. These polyps attach themselves to a hard limestone base and essentially duplicate themselves.

There are two main types of corals—soft and hard. Soft corals tend to look more like grass or plants swaying in the breeze. Because they don’t have a hard exoskeleton, they exhibit more movement. Hard corals look more like rocks and have two general distinctions: the large polyp stony corals (or LPS) and the small polyp stony corals (or SPS). The main difference is the size of the polyps; LPS has bigger, fleshy-looking polyps, whereas SPS polyps are smaller.

These corals are deemed good to start with because they’re not quite so finicky about light and water quality. Bear in mind that even though Zoanthids are commonly recommended for beginners because they’re relatively easy to maintain, there are also certain types that can produce a dangerous toxin that can spread in the air.

Feeding

Corals can be self-sufficient about eating, but only up to a point. They have a symbiotic relationship with tiny algae called zooxanthellae algae. In return for a safe place to dwell inside the corals, the algae provide nourishment for corals through photosynthesis. But not all corals are photosynthetic, and photosynthesis isn't enough for those that are.

That’s why other methods are needed to round out a coral’s diet. One way is through direct feeding, which means feeding like you would a fish. It may take some experimenting to learn which food your coral responds to, but phytoplankton and bits of small fish are possibilities. Also, look for commercially available coral foods and concentrates. Then there’s the hands-off approach of indirect feeding, when corals consume waste products and uneaten food meant for fish.

Lighting

You can’t have photosynthesis without light, but different types of corals have different lighting requirements. The wattage depends on the type of coral. Soft corals and LPS corals are more adaptable to changes in light, so they can make do with less wattage. This isn’t so true for SPS corals, however, which demand a greater wattage. You’ll also want to consider the color spectrum your lights employ and how they will impact your corals’ appearance. 

The desired lighting will also dictate where you place the coral in the tank. Because SPS corals like more intense light, you can place them closer to the top of the tank. LPS and soft corals can manage lower down.

Interactions

To ensure fish won’t eat your corals, look into non-aggressive reef-safe fish—certain species of angelfish, clownfish, tangs and gobies—and janitors. Janitors—including shrimp, hermit crabs, and sea urchins—have the added benefit of built-in tank maintenance because they keep the glass and substrate-free of debris and help keep a high water quality.

Corals can also encounter problems from other corals. They can be territorial, and different species can sting each other with tentacles, release harmful chemicals, or even eat each other. That’s why important to properly space them in the tank and monitor their growth.

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