What is the difference between stony and soft coral reefs? Are all corals the same? Some corals have a hard skeletal system, while others don’t. And that is the main difference between hard, soft corals, and stony corals. However, often the lines get a bit blurred, since even aggressive corals can appear to be fleshy and soft. So, let’s take a closer look at what makes an aggressive coral stony. Ultimately, it boils down to whether the reef has a hard skeletal system. If the coral reef does have a calcium carbonate skeletal system that the polyps extend from, it’s considered a stony coral. Even if that polyp is large, fleshy, and sways back and forth.
Small-polyp stony corals (SPS) have little polyps extending out of their hard skeleton. They don’t really sway or move, and they don’t appear very fleshy. Large-polyp stony reefs (LPS) still have a hard skeletal base that their larger fleshy polyps protrude from. And because they can be fleshy and large, they might seem soft and easily sway back and forth in the current. However, since they still extend out of a tough calcium carbonate skeletal system, they are considered to be a stony coral reef. If that coral were to die and the fleshy polyps melted away, a hard skeletal system would still remain.
On the other hand, soft corals do not have a hard skeletal system. Instead, their soft, fleshy bodies are filled with small spear-shaped spicules made from calcium carbonate that help to add rigidity to their soft, fleshy bodies while they’re expanded. If that reef were to die and melt away, there would be no skeletal system left behind. And while you may find a few small spicules here and there, chances are, there would be no trace the reef was ever there at all. The only real exception to that rule, which I did mention earlier, would be gorgonians and sea fans that do leave behind a sort of flexible skeletal system.
Unlike the hard and rigid calcium carbonate skeletons of stony corals, their skeletal systems are usually dark brown or black, super thin, and very bendy. The next big question is, is there a difference in stony and soft coral care in a coral reef tank? Yes, there definitely is a difference. And when it comes to caring for corals in a reef tank, stony corals tend to be more demanding than soft corals, especially for those who are newer to the hobby.
Because they don’t have a true skeleton, soft corals tend to be much less demanding of alkalinity and calcium. Soft corals also tend to come from nutrient-rich environments that are dirty and silty, so many soft corals have no problem in a reef aquarium that has high nutrients and isn’t dosed very often. In other words, they are very resilient and typically do just fine in a tank with less than optimal conditions for stony corals. They’re also often less demanding of intense lighting, so you can easily keep them without getting high-end lights. With that being said, having a good reef light is going to have a pretty big impact on how vibrant most of those soft corals will be.
Large-polyp stony corals (LPS) are a great place to start for reefers who want to get into stony corals. While they will definitely require you to test your aquarium at least weekly and dose additives to maintain the levels of two major elements, alkalinity and calcium, many LPS do appreciate higher nutrients, similar to soft corals, and do just fine with similar light conditions. LPS, however, can also benefit quite a lot from proper circulation, so ensuring you have a capable wave pump or pumps is also going to be important. Now, small-polyp stony corals (SPS) are considered to be the most challenging corals to keep.
They are the most sensitive to water parameters, require stable conditions with optimal levels of not only the major elements but also minor and trace elements. Many of them, especially acropora, require pristine water with just the right level of nutrients in order to thrive and look their best. They often require the most intense lighting, as well as the most intense and thoughtfully-implemented flow. An aquarium designed for SPS corals is going to be the most challenging and often the most expensive in terms of equipment and additives. If a soft reef is mini golf, an SPS reef is Formula One. An SPS reef is Formula One if a soft coral reef is go-karting.
I’m sure you get the idea if a soft coral reef is. What about mixed coral reef tanks? Mixed reefs are the ones that have a bit of everything. Softies, LPS, and SPS. They are truly the most challenging reef tanks to keep happy because you’re trying to naturally balance the needs of all three types of corals in a single environment. It is a major challenge, and one that I’ve taken on many, many times. It can be very rewarding and also seriously frustrating. In my humble opinion, a mixed reef is definitely the most challenging reef to maintain.