Remember that real estate on a natural reef is a finite commodity and corals fight for space for survival everyday. This is also true for our captive reefs that we are trying to duplicate in our aquariums. Corals depend on open spaces on the reef for growth, expansion, and for general survival. Being that this space is limited, over thousand of years corals have found ways to expand on it's or other corals territory for survival. This process is what i call coral warfare and there are basically four ways that corals accomplish this. Fast Growth Method
These corals grows rapidly and fight for space by growing over corals and blocking the all important light form reaching below to it's neighbors that is critical for survival. Many of the corals will encrust and smother the competing corals directly. Digestive Method
These corals will send out digestive organs and kill their neighbors simply by ingesting them, gaining nutrition and energy all while taking the new area of the dead corals. Stinger Tentacles
Other corals sends out stinger tentacles a good distant away from the mother corals. This stinging process will inhibit their neighbors from growing and in turn give the advantage to the mother corals for space to grow. Chemical Warfare Method
These corals will emit harmful chemicals into the water column, poisoning their neighbors to death. In doing so these types of corals will gain advantage on the all important real estate for growth.
Knowing this, what are the ways to keep these animals in relative harmony in our closed system? Well there are several things we need to employ to be successful. The first thing is to determine which process of survival the coral uses and address them by.
Consider generous space for fast growth corals. Place other corals a decent distance from each other leaving space for growth. In time you will need to cut back these growers just like any garden in and around your house to keep them in check. You will also not want to place light loving corals under these growers otherwise in time these fast growers will block the required light needed for those corals to survive and death of those neighbors will be inevitable. If the corals uses digestive or stinger method you need to consider placing like corals as neighbors, and making generous space between corals. If you decide to keep corals that uses chemical warfare you will need to use carbon as a way to remove deadly toxins in the water column from killing other corals in the aquarium. You will need to use a combination of these solutions to keep all these corals together in the same aquarium. Hope this helps Happy Reefing!