As you work to recreate a natural environment in your fish tank for your tropical saltwater fish, one way to make it feel more like home is to put some coral in the tank. Many fish kept in home aquariums are from coral reefs, and you can attempt to recreate this as you decorate the tank. There are three common ways to do this: with live coral, a coral reef, or dead coral.
Live coral is much more than a decoration - it is actually an invertebrate organism. As such, it has stringent light requirements. There are over 500 different species of coral in the world, each with its own unique needs. Before you purchase live coral for your tank, research the light and water requirements for that particular species, and make sure that it will feel "at home" in your aquatic environment. Choose a live coral that fits your tank's parameters, rather than choosing based on shape or color alone. Keep in mind that you may need to supplement the tank's diet with food that the coral likes, such as phytoplankton, shrimp, squid, or krill.
If you have had success with adding a few individual live corals to your tank and the water quality is stable, consider building a coral reef. This is a collection of corals that create a stunning display of color and shape variety, providing your fish with plenty of places to hide in the tank. Add reef supplements to the tank to keep the corals healthy. These include iodine, calcium, buffer, and strontium/molybdenum.
"Dead coral" is actually the skeleton of a once-living coral. These can have a place in the saltwater aquarium, although live coral will always be more beautiful and realistic looking. Dead coral is often used in fish only tanks. It requires little maintenance and does not react to water changes, so it is often the decoration of choice for beginners who are still cycling their tanks. However, once the tank is established, consider adding to the environment with live coral or live rock.