Soft corals – what is it?

Soft corals are a group of fascinating marine organisms belonging to the subclass Octocorallia. Unlike stony corals, which build massive calcium carbonate skeletons that form the foundation of coral reefs, soft corals do not produce such rigid structures. Instead, they possess flexible, leathery bodies that sway gracefully in the water currents, giving aquariums and natural reefs a sense of movement and life. They are composed of colonies of polyps, each one a small organism, and together they form structures that can resemble trees, bushes, or even delicate fans. A distinguishing feature is the presence of tiny internal structures called spicules, which provide some support but still keep them soft. Their colors range from subtle pastels to vibrant purples, reds, and yellows, and many species exhibit bioluminescent properties under actinic lighting. Due to their resilience, faster growth compared to many SPS corals or LPS corals, and reduced demand for intense lighting and precise calcium supplementation, soft corals are considered excellent choices for beginner and intermediate aquarists who want to bring the beauty of the reef into their tanks without the high maintenance often required by hard corals.

Soft corals in the aquarium environment

The presence of soft corals in an aquarium transforms the entire aquascape into a living, breathing ecosystem that appears more natural and dynamic. Their polyps extend into the water, swaying with even the slightest current, which not only creates a visually captivating effect but also plays a functional role in the health of the aquarium. Many soft corals harbor symbiotic algae known as zooxanthellae within their tissues. These algae conduct photosynthesis, providing the coral with essential nutrients while benefiting from the coral’s waste products in return. This symbiotic exchange contributes to their resilience and explains why soft corals often thrive in a wide range of water conditions. An aquarist maintaining a 200-liter system, for example, may introduce a variety of species such as Leather corals, Colt corals, and Zoanthids. These corals not only add color but also help stabilize the ecosystem by taking up dissolved nutrients. An interesting calculation shows that a healthy colony of soft corals can process measurable amounts of dissolved organic matter every day, acting as natural filters that improve overall water quality. Compared to the strict requirements of SPS species that demand calcium concentrations around 420 ppm and alkalinity in a narrow range, soft corals usually tolerate fluctuations, making them less demanding. Their adaptability allows aquarists to experiment with aquascape designs, mixing them with fish, crustaceans, and other reef organisms without the risk of sudden collapse due to minor parameter shifts. However, their ability to release chemical compounds into the water, known as allelopathy, means careful planning is required when placing them near other corals. Many aquarists use activated carbon and protein skimmers to reduce these compounds, ensuring harmony in a mixed reef tank. A thriving display dominated by soft corals may resemble an underwater garden, with colonies stretching, bending, and creating continuous motion that enhances the observer’s sense of immersion in a true reef environment.

Types, growth, and care of soft corals

When discussing the classification of soft corals, it is worth highlighting their extraordinary diversity. Within aquariums, one can encounter varieties such as Sarcophyton (commonly known as Leather corals), Cladiella (Colt corals), Sinularia, Zoanthus (Zoanthids), and Palythoa. Each of these exhibits distinctive morphology, ranging from tree-like branching to mat-forming colonies that spread across live rock. Their growth rates can be astonishing; under adequate lighting and stable parameters, some species double in size within just a few months. A colony of Zoanthids, for instance, may start with 10 polyps but, within half a year, spread into a lush mat covering several hundred square centimeters of rock. This rapid propagation makes them highly rewarding, especially for aquarists who enjoy trading or fragmenting corals. In terms of care, soft corals usually thrive under moderate lighting—about 50–150 PAR—and moderate to strong water flow that prevents detritus accumulation. Strong flow also encourages polyps to open fully, enhancing their photosynthetic efficiency. Feeding can be achieved indirectly; while they rely heavily on photosynthesis, many species benefit from dissolved organic matter and the occasional addition of planktonic foods such as rotifers, phytoplankton, or marine snow. Proper placement within the tank is crucial; for example, Leather corals tend to expand significantly, and their broad caps may shade other specimens below. Strategic aquascaping ensures that every coral receives optimal conditions. Successful care involves consistent monitoring of salinity around 1.025, temperatures between 24°C and 27°C, and nutrient levels balanced so that nitrate and phosphate remain detectable but not excessive. Interestingly, aquarists often find that soft corals serve as indicators of tank stability. If they close up for more than 48 hours, it often suggests fluctuations in water chemistry. On the other hand, fully extended polyps reflect a thriving, balanced environment. Their adaptability and growth make them perfect for aquarists aiming to create lush reefscapes where life seems to expand exponentially, with every square centimeter eventually occupied by vibrant, pulsating colonies of soft corals.